WO2013059670A2

WO2013059670A2 - Octahedral and pyramid-on-post tips for microscopy and lithography

Info

Publication number: WO2013059670A2
Application number: PCT/US2012/061132
Authority: WO
Inventors: Raymond Roger Shile
Original assignee: Nanoink, Inc.
Priority date: 2011-10-21
Filing date: 2012-10-19
Publication date: 2013-04-25
Also published as: WO2013059670A3

Abstract

A device comprises a cantilever, and an octahedral tip extending from a bottom surface of the cantilever. The octahedral tip comprises a top portion at which the octahedral tip is attached to the cantilever, a bottom portion comprising a first vertex, and a middle portion disposed between the top portion and the bottom portion, the middle portion comprising four additional vertices and being wider than the top portion and the bottom portion. Another device comprises a cantilever, and a tip extending from a bottom surface of the cantilever. The tip comprises an elongated post portion and a pyramidal portion located at one end of the elongated post portion. The cantilever and the tip are formed of a continuous layer of material having a thickness between 400 nm and 1000 nm.

Description

OCTAHEDRAL AND PYRAMID-ON-POST TIPS FOR MICROSCOPY

AND LITHOGRAPHY

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Serial Number 61/550,305 filed October 21, 2011, the complete disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND

Microscale tips and nanoscale tips can be used for high resolution patterning, imaging, and data storage. In patterning or printing, an ink or patterning compound can be transferred from the tip to a surface such as a substrate surface. For example, the tip can be a scanning probe microscope (SPM) tip, such as an atomic force microscope (AFM) tip, attached to one end of a cantilever or a larger support structure. Dip-Pen Nanolithography (DPN) patterning is a promising technology for patterning inks and nanomaterials which can be carried out via different embodiments including use of AFM tips and cantilevers. Alternatively, tips can be used without cantilevers to support the tips.

These direct-write nanolithographic approaches can provide advantages which competing nanolithographies may not provide, such as high registration, throughput, multiplexing, versatility, and lower costs. Various approaches are described in, for example, Mirkin et al, WO 00/41213; WO01/91855; U.S. Patent Application Pub. No. 2009/0325816; Small, 2005, 10, 940-945; Small, 200901538; U.S. Pat. Nos. 7,005,378; 7,034,854; 7,060,977; 7,098,056; and 7,102,656; and U.S. Patent Application Pub. No. 2009/0205091 to Nanolnk.

Pens used for patterning and printing may be formed as cantilevers having pyramidal tips. Such pens can be fabricated by first defining a square opening in a suitable masking material, such as silicon dioxide or silicon nitride, on the surface of an oriented silicon mold wafer. The wafer is then immersed in a crystallographic etchant such as potassium hydroxide (KOH), resulting in pyramidal pits within the mask openings. These pits serve as a tip mold for low stress silicon nitride or other material subsequently deposited, typically by chemical vapor deposition.

Silicon nitride with low stress gradient can be then deposited onto the mold wafer to form a cantilever and tip. The nitride thickness may be about 600 nm. Then, a handle wafer, typically made of Pyrex or borosilicate glass, may be bonded to the surface of the silicon nitride, and the silicon mold wafer is etched away, typically with KOH or tetramethylammonium hydroxide (TMAH). This results in a free-standing cantilever with a pyramidal tip, the cantilever extending from the handle wafer. These tips are typically very sharp, with radii less than 50 nm at the convergence of the four crystallographic plans of the tip.

The tip radius can be reduced even further with an additional oxidation step. For example, after the pyramidal pits are formed, the masking oxide can then be stripped and the wafers re-oxidized at 950°C for 180 minutes to grow about 5,50θΑ of silicon oxide. At this time and temperature, the oxide at the bottom of the pit is hindered with respect to growth, and thus when a cast film is deposited in this pit, the tip sharpness can approach a 10 nm tip radius or smaller.

Such pens are described, for example, in T. R. Albrecht, S. Akamine, T. E. Carver, and C. F. Quate, "Micro fabrication of cantilever styli for the atomic force microscope," J. Vac. Sci. Technol. A, Vac. Surf. Films (USA), 1990; and S. Akamine, and C. F. Quate, "Low temperature oxidation sharpening of microcast tips," J. Vac. Sci. Technol B., vol. 10, No. 5, Sep/Oct 1992.

However, the shape and height of the tips formed by this process are limited by the crystallographic etching step. Since the pyramidal tip is bounded by four planes inclined at 54.74 degrees (due to the crystallographic etching), the tip height is limited and equal to 0.71 times the base dimension of the square defined in the mask.

U.S. Patent Publication No. 2009/0173712 discusses a method of fabricating a cantilever type probe and a method of fabricating a probe card. However, this references does not provide advantages of the methods and devices disclosed herein.

A need exists to develop lithography pens with different possible tip shapes and tip heights, and methods of manufacturing such pens.

SUMMARY

Embodiments described herein include devices and instruments, and methods of making and using such devices and instruments.

In one embodiment, a device comprises a cantilever; and an octahedral tip extending from a bottom surface of the cantilever. The octahedral tip comprises a top portion at which the octahedral tip is attached to the cantilever, a bottom portion comprising a first vertex, and a middle portion disposed between the top portion and the bottom portion, the middle portion comprising four additional vertices and being wider than the top portion and the bottom portion.

In another embodiment, a device comprises a cantilever; and a tip extending from a bottom surface of the cantilever. The tip comprising an elongated post portion and a pyramidal portion located at one end of the elongated post portion. The cantilever and the tip are formed of a continuous layer of material having a thickness between 400 nm and 1000 nm.

In another embodiment, a method comprises providing a silicon mold wafer;

forming a vertical pit in the silicon mold wafer using reactive ion etching; forming an octahedral pit from the vertical pit using crystallographic etching, the octahedral pit comprising a top portion near a top surface of the silicon mold wafer, a bottom portion comprising a first vertex, and a middle portion disposed between the top portion and the bottom portion, the middle portion comprising four additional vertices and being wider than the top portion and the bottom portion; and forming a cantilever and an octahedral tip by depositing a deposition material on a portion of the top surface of the silicon mold wafer and on an inner surface of the octahedral pit.

In another embodiment, a method comprises providing a silicon mold wafer;

forming a vertical pit in the silicon mold wafer using reactive ion etching; forming an oxide layer on side and bottom surfaces of the vertical pit; removing the oxide layer from the bottom surface of the vertical pit; forming a pyramidal pit in the bottom surface of the vertical pit using crystallographic etching; and forming a cantilever and a tip by depositing a deposition material on a portion of a top surface of the silicon mold wafer and on inner surfaces of the vertical pit and the pyramidal pit.

In another embodiment, a method comprises providing a device comprising a cantilever; and an octahedral tip extending from a bottom surface of the cantilever. The octahedral tip comprises a top portion at which the octahedral tip is attached to the cantilever, a bottom portion comprising a first vertex, and a middle portion disposed between the top portion and the bottom portion, the middle portion comprising four additional vertices and being wider than the top portion and the bottom portion. The method further comprises transferring an ink or patterning compound from the octahedral tip to a substrate surface.

In another embodiment, a method comprises providing a device comprising a cantilever; and a tip extending from a bottom surface of the cantilever, the tip comprising an elongated post portion and a pyramidal portion located at one end of the elongated post portion. The cantilever and the tip are formed of a continuous layer of material having a thickness between 400 nm and 1000 nm. The method further comprises transferring an ink or patterning compound from the tip to a substrate surface.

A device with the octahedral tip provides several advantages over prior art devices with, for example, pyramidal tips. One advantage for at least one embodiment is that the height of the octahedral tip is not limited by the base dimension of the square defined in the masking layer. Instead, the use of two different etching process— for example, a reactive ion etch process following by a crystallographic etch process— removes the previous restraints on tip height. Using an octahedral tip, the tip height is limited only by the depth achieved during the reactive ion etching process. The resulting mold takes the form of an irregular octahedron with a height of d + 0.71w, wherein d is the depth of the pit etched by reactive ion etching, and w is the width of the opening in the masking layer.

A second advantage for at least some embodiments is that octahedral tips include four side vertices, which can be used in various applications. For example, the side vertices may be used in atomic force microscopy to profile surfaces that are vertical relative to the cantilever. The side vertices may also be used in nanolithography applications to transfer ink from the side vertices to surfaces that are vertical relative to the cantilever.

A third advantage for at least some embodiments is that the octahedral tips have a larger surface area than typical pyramidal tips, and can therefore hold more ink than pyramidal tips, allowing for more efficient patterning of the ink onto a substrate surface.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a process flow diagram showing a method of manufacturing a cantilever with an octahedral tip according to one embodiment.

FIG. 2 is a top, front perspective view of an octahedral tip according to one embodiment.

FIG. 3 depicts a process flow diagram showing a method of manufacturing a cantilever with a "pyramid-on-post" tip according to one embodiment.

FIG. 4 is a top, front perspective view of a "pyramid-on-post" tip according to one embodiment.

FIG. 5 is a front, cross-sectional view of a mold wafer with pits that can be used during manufacturing of the "pyramid-on-post" tip depicted in FIG. 3.

FIG. 6A is an SEM image showing a front, bottom perspective view of an octahedral tip attached to a triangular cantilever that was made according to one embodiment. FIG. 6B is an SEM image showing a front, bottom perspective view of an octahedral tip attached to a triangular cantilever that was made according to one embodiment, where the tip is slightly shorter than the tip shown in FIG. 6A.

FIG. 6C is an SEM image showing a close-up side view of a side vertex of an octahedral tip that was made according to one embodiment.

FIG. 7A is an SEM image showing a rear, side, bottom perspective view of a "pyramid-on-post" tip attached to a triangular cantilever that was made according to one embodiment.

FIG. 7B is an SEM image showing a front, bottom perspective view of a "pyramid- on-post" tip attached to a triangular cantilever that was made according to one embodiment.

FIG. 7C is an SEM image showing a front, bottom perspective view of a "pyramid- on-post" tip attached to a triangular cantilever that was made according to one embodiment, where a pyramid portion of the tip extends past a post portion of the tip.

DETAILED DESCRIPTION

Introduction

For practice of the various embodiments described herein, lithography,

microlithography, and nanolithography instruments, pen arrays, active pens, passive pens, inks, patterning compounds, kits, ink delivery, software, and accessories for direct-write printing and patterning can be obtained from Nanolnk, Inc., Skokie, IL. Instrumentation includes, for example, the NSCRIPTOR and DPN5000. Software includes, for example, INKCAD software (Nanolnk, Chicago, IL), providing user interface for lithography design and control. E-Chamber can be used for environmental control. Dip Pen Nanolithography^® and DPN^® are trademarks of Nanolnk, Inc.

The following patents and co-pending applications are related to direct-write printing with use of cantilevers, tips, and patterning compounds, and related

instrumentation, and can be used in the practice of the various embodiments described herein, including inks, patterning compounds, software, ink delivery devices, and the like. All references cited herein are incorporated by reference in their entirety.

U.S. Patent No. 6,635,311 to Mirkin et al, which describes fundamental aspects of DPN printing including inks, tips, substrates, and other instrumentation parameters and patterning methods; U.S. Patent No. 6,827,979 to Mirkin et al., which further describes fundamental aspects of DPN printing including software control, etching procedures, nanoplotters, and complex and combinatorial array formation.

U.S. patent publication number 2002/0122873 Al published September 5, 2002 ("Nanolithography Methods and Products Produced Therefore and Produced Thereby"), which describes aperture embodiments and driving force embodiments of DPN printing.

U.S. Patent No. 7,279,046 to Eby et al. ("Methods and Apparatus for Aligning Patterns on a Substrate"), which describes alignment methods for DPN printing.

U.S. Patent No. 7,060,977 to Dupeyrat et al. ("Nanolithographic Calibration Methods"), which describes calibration methods for DPN printing.

U.S. Patent Publication 2003/0068446, published April 10, 2003 to Mirkin et al. ("Protein and Peptide Nanoarrays"), which describes nanoarrays of proteins and peptides.

U.S. Patent No. 7,361,310 to Mirkin et al. ("Direct- Write Nanolithographic

Deposition of Nucleic Acids from Nanoscopic Tips"), which describes nucleic acid.

U.S. Patent No. 7,273,636 to Mirkin et al. ("Patterning of Solid State Features by Direct- Write Nanolithographic Printing"), which describes reactive patterning and sol gel inks (now published August 28, 2003 as 2003/0162004).

US Patent Nos. 6,642,129 and 6,867,443 to Liu et al. ("Parallel, Individually Addressable Probes for Nanolithography"), describing active pen arrays.

U.S. Patent Publication 2003/0007242, published January 9, 2003 to Schwartz ("Enhanced Scanning Probe Microscope and Nanolithographic Methods Using Same").

U.S. Patent Publication 2003/0005755, published January 9, 2003 to Schwartz ("Enhanced Scanning Probe Microscope").

U.S. Patent No. 7,093,056 to Demers et al, describing catalyst nanostructures and carbon nanotube applications.

U.S. Patent 7,199,305 to Cruchon-Dupeyrat et al, and U.S. Patent No. 7,102,656 to Mirkin et al., describing printing of proteins and conducting polymers respectively.

U.S. Patent No. 7,005,378 to Crocker et al., describing conductive materials as patterning compounds.

U.S. Patent Application 10/689,547 filed October 21, 2003, now published as 2004/0175631 on September 9, 2004, describing mask applications including photomask repair.

U.S. Patent No. 7,034,854 Cruchon-Dupeyrat et al., describing microfluidics and ink delivery. U.S. Patent Application 10/788,414 filed March 1 , 2004, now published as

2005/0009206 on January 13, 2005 describing printing of peptides and proteins.

U.S. Patent No. 7,326,380 to Mirkin et al, describing ROMP methods and combinatorial arrays.

U.S. Patent No. 7,491,422 to Zhang et al, describing stamp tip or polymer coated tip applications.

U.S. Patent Application 11/065,694 filed February 25, 2005, now published as 2005/0235869 on October 27, 2005, describing tipless cantilevers and flat panel display applications.

US Patent publication 2006/001,4001 published January 19, 2006 describing etching of nanostructures made by DPN methods.

WO 2004/105046 to Liu & Mirkin published December 2, 2004 describes scanning probes for contact printing.

US Patent Application "Active Pen Nanolithography," 11/268,740 to Shile et al. filed November 8, 2005 describes for example thermcompression bonding and silicon handle wafers.

DPN methods are also described in Ginger et al., "The Evolution of Dip-Pen Nanolithography," Angew. Chem. Int. Ed. 2004, 43, 30-45, including description of high- throughput parallel methods. See also Salaita et al., "Applications of Dip-Pen

Nanolithography," Nature Nanotechnology, 2007, Advanced On-line publication (11 pages).

Direct write methods, including DPN printing and pattern transfer methods, are described in for example Direct-Write Technologies, Sensors, Electronics, and Integrated Power Sources, Pique and Chrisey (Eds), 2002.

Scanning probe microscopy is reviewed in Bottomley, Anal. Chem., 1998, 70, 425R- 475R. Also, scanning probe microscopes are known in the art including probe exchange mechanisms as described in, for example, US Patent No. 5,705,814 (Digital Instruments).

Microfabrication methods are described in for example Madou, Fundamentals of Microfabrication, 2^nd Ed., 2002, and also Van Zant, Microchip Fabrication, 5^th Ed., 2004.

US Patent No 6,827,979 to Mirkin et al., discusses DPN using atomic force microscope (AFM) tips.

US Patent Publication 2003/0022470 and Publication 2006/0228873 to Liu et al. describe cantilever fabrication methods. US Patent Publication 2006/0040057 to King, Sheehan et al. describes thermal DPN printing methods.

U.S. Provisional Applications No. 61/052,864, filed May 13, 2008, and U.S.

Provisional Application No. 61/167,853, filed April 8, 2009, are also both incorporated by reference in their entireties.

See also, commercial printing pen and pen array products, as well as printing instruments, and other related accessories, commercially available from Nanolnk, Inc.

(Skokie, IL).

Devices with Octahedral Tips

One embodiment provides an octahedral tip. In one embodiment, a device comprises a cantilever and an octahedral tip extending from a bottom surface of the cantilever.

In one embodiment, the method of making the device is shown in Figs. 1(a) through 1(h). Figs. 1(a) through 1(h) are cross-sectional views taken along a central axis of the cantilever and octahedral tip.

First, referring to Fig. 1(a), a mold wafer 110 is provided. The mold wafer 110 may be made of a crystalline material such that anisotropic etching may be performed on the mold wafer. For example, the mold wafer 110 may be made of single crystalline silicon. Other possible materials for the mold wafer include A masking layer 112 is formed on the surface of the oriented a mold wafer 110. The masking layer 112 is preferably formed using contact or projection optical lithography, though other methods, such as electron-beam and x-ray lithography, may be used. The masking layer 112 may be, for example, a thin film of silicon dioxide or silicon nitride. Other possible masking layer materials include gold, chrome, aluminum oxide, and boron nitride. The thickness of the masking layer may be, for example, between 5000 and 5500 A. An opening 114 is formed in the masking layer 112 such that a portion of the mold wafer 110 is exposed. The opening 114 is preferably square. The openings can be of any size. For example, they can be between about 1 micron to about 60 microns, or between about 2 microns to about 50 microns.

Next, referring to Fig. 1(b), an anisotropic etching process is performed using the masking layer 112 as an etching mask to form a vertical pit 116. The vertical pit 116 may be formed using reactive ion etching (RIE). For example, an STS Inductively Coupled (ICP) RIE system may be used with 40 seem SF₆, 40 seem 0₂, a platen power of 10 watts, a coil power of 500 watts, a pressure of about 20 mTorr, and no parameter switching.

Examples of processing gases used during this etching process include SF₆, CF₄, NF₃, Cl₂, and Br₂. Alternatively a Bosch process may be employed in which alternating etch and passivation cycles are used. When the opening 114 is square, the vertical pit 116 has the shape of a right rectangular prism with four side surfaces 118 and a bottom surface 120.

Then, referring to Fig. 1(c), a crystallographic wet etching process is performed so as to etch an ansiotropically octahedral pit 122. To form the octahedral pit 122 from the vertical pit 116, the mold wafer 110 may be immersed in a wet etchant such as potassium hydroxide (KOH), tetramethyl ammonium hydroxide (TMAH), or an aqueous solution of ethylene diamine and pyrocatechol (EDP). When such wet etchants are used, the rate at which etching occurs depends on the orientation of the crystalline mold wafer. Thus, when the mold wafer is oriented in specific manner, it becomes possible to create an octahedral pit 122, with five vertices. For example, the mold wafer may be sliced on the (100) plane, with the mask opening aligned with the (110) oriented flat of the wafer. A top portion 124 of the octahedral pit 122 is the portion near the top surface of the mold wafer 110, through which the wet etchant enters the vertical pit 116 to form the octahedral pit 122. The bottom portion 126 of the octahedral pit 122 contains a first, bottom vertex 128. The middle portion 130 of the octahedral pit 122 is the portion between the top portion 124 and bottom portion 126, and contains four side vertices 132. The middle portion 130 is wider than the top portion 124 and the bottom portion 126. The four side vertices 132 may form a square in a plane that is parallel to the plane of the top surface of the mold wafer 110.

Next, referring to Fig. 1(d), the masking layer 112 is stripped from the surface of the mold wafer 110.

Referring the Fig. 1(e), the mold wafer 110 may then optionally be oxidized at a temperature between 950° C and 1100° C for about six hours to grow a tip-sharpening oxidation layer 134 of silicon dioxide on the inner surfaces of the octahedral pit 122. At this time and temperature, the oxide at the bottom of the pit is hindered with respect to growth, and thus when a cast film is deposited in this pit, the tip sharpness can approach a 10 nm tip radius or smaller. The tip-sharpening oxidation layer 134 may have a thickness of about 3900 A.

Next, referring to Fig. 1(f), a deposition material layer 136 is then formed on the inner surfaces of the octahedral pit 122 and on the top surface of the mold wafer 110. The deposition material layer 136 will form the cantilever and octahedral tip. The deposition material layer 136 may, for example, be made of silicon nitride or silicon carbide. The deposition material layer 136 may have a thickness of about 400 to 1000 nm, and preferably between 500 nm and 700 nm, more preferably about 600 nm. The deposition material layer 136 is patterned and aligned such that the end of the cantilever lies over the octahedral pit 122. The deposition material layer 136 may, for example, be deposited using chemical vapor deposition (CVD), sputtering, evaporation, or plating. For example, a typical low stress silicon nitride LPCVD process may use 95 seem Dichlorosilane, and 200 seem

Ammonia, at a temperature 775° C and a pressure of 200 mTorr.

Referring to Fig. 1(g), a handle wafer 138 may then optionally be bonded to the deposition material layer 126. The handle wafer 138 may, for example, be made of Pyrex or another borosilicate glass.

Finally, referring to Fig. 1(h), the mold wafer 110 is etched away using, for example, KOH, TMAH, EDP, HF/HN0₃, or XeF₂, which results in a free-standing cantilever 140 with an tip 142 have the shape of an octahedron extending from a bottom surface of the cantilever 140. Of course, due to this attachment, the octahedral tip 142 does not have the shape of a perfect octahedron. Rather, the top of the octahedron is truncated at the location where the octahedral tip 142 extends from the cantilever 140. The cantilever 140 and octahedral tip 142 are integral, both being made of the single layer of deposition material. The octahedral tip 142 has top portion 144, where the octahedral tip 142 is attached to the cantilever 140. The octahedral tip has a bottom portion 146 which includes a first, bottom vertex 148. Between the top portion 144 and the bottom portion 146 is a middle portion 150, which includes four side vertices 152, two of which are visible in Fig. 1(h). The middle portion 150 may be wider than the top portion and the bottom portion. The four side vertices 152 of the middle portion 150 may form a square in a plane that is parallel to the plane of the cantilever 140. Because the octahedral tip 142 and cantilever 140 are formed of a single thin layer of deposition material, the octahedral tip 142 is hollow. The width of the cantilever may be under 1000 microns, for example, about 25 microns. The length of the cantilever may also be under 1000 microns, for example, about 200 microns. The thickness of the cantilever may be between about 400 and 1000 nm, for example, about 600 nm. The octahedral tips may, for example, have a height between 5 and 20 microns and a width (between vertices) between 10 and 20 microns.

Devices with "Pyramid-on-Post" Tips

Another embodiment provides "pyramid-on-post tips" as described herein. In another embodiment, a device comprises a cantilever and a "pyramid-on-post" tip extending from a bottom surface of the cantilever. The method of making the device is shown in Figs. 3(a) through 3(i). Figs. 3(a) through 3(i) are cross-sectional views taken along a central axis of the cantilever and octahedral tip.

The first steps used to make a device with a pyramid-on-post tip are the same as those used to make a device with the octahedral tip, described above. First, referring to Fig. 3(a), a mold wafer 210 is provided. The mold wafer 210 may be made of a crystalline material such that anisotropic etching may be performed on the mold wafer. For example, the mold wafer 210 may be made of single crystalline silicon. A masking layer 212 is formed on the surface of the oriented a mold wafer 210. The masking layer 112 is preferably formed using contact or projection optical lithography, though other methods, such as electron-beam and x-ray lithography, may be used. The masking layer 112 may be, for example, a thin film of silicon dioxide or silicon nitride. Other possible masking layer materials include gold, chrome, aluminum oxide, and boron nitride. The thickness of the masking layer may be, for example, between 5000 and 5500 A. An opening 114 is formed in the masking layer 112 such that a portion of the mold wafer 110 is exposed. The opening 114 is preferably square. The openings can be of any size. For example, they can be between about 1 micron to about 60 microns, such as between about 2 microns to about 50 microns.

Next, referring to Fig. 3(b), an anisotropic etching process is performed using the masking layer 112 as an etching mask to form a vertical pit 116. The vertical pit 116 may be formed using reactive ion etching (RIE). For example, an STS Inductively Coupled (ICP) RIE system may be used with 40 seem SF₆, 40 seem 0₂, a platen power of 10 watts, a coil power of 500 watts, a pressure of 20 mTorr, and no parameter switching. Examples of processing gases used during this etching process include SF₆, CF₄, NF₃, Cl₂, and Br₂.

Alternatively a Bosch process may be employed in which alternating etch and passivation cycles are used. When the opening 114 is square, the vertical pit 116 has the shape of a right rectangular prism with four side surfaces 118 and a bottom surface 120.

Then, referring to Fig. 3(c), an oxide layer 222 is grown on the inner surfaces of the vertical pit 216. The oxide layer may be grown in steam at a temperature of about 1100° C. The oxide layer 222 is removed from the bottom surface 220 of the vertical pit 216 using reactive ion etching, but remains on the side surfaces 218 of the vertical pit 216. Because the top surface of the mold wafer 210 already has a masking layer 212, when the oxide layer 222 is grown, the masking layer 212 on the top surface of the mold wafer 210 is thicker than the oxide layer 222 on the side and bottom surfaces of the vertical pit 216. Thus, when the duration of the reactive ion etching is carefully controlled, it becomes possible to clear the bottom surface 220 of the vertical pit 216 without removing the masking layer 212 from the top surface of the mold wafer 210. For example, an STS Inductively Coupled (ICP) RIE system may be used with 100 seem CF₆, 45 seem 0₂, a platen power of 12 watts, a coil power of 800 watts, a pressure of about 50 mTorr, and no parameter switching

Then, referring to Fig. 3(d), a crystallographic wet etching process is performed so as to etch an ansiotropically pyramidal pit 224. To form the pyramidal pit 224, the mold wafer 110 may be immersed in a wet etchant such as KOH, TMAH, or EDP. As discussed above, when such wet etchants are used, the rate at which etching occurs depends on the orientation of the crystalline mold wafer. Because the side surfaces 218 are protected from the wet etchant by the oxide layer 222, a pyramidal pit 224 can be formed in the bottom surface 220 of the vertical pit 216. To do this, the mold wafer may be sliced on the (100) plane.

Next, referring to Fig. 3(e), the masking layer 212 and oxide layer 222 are stripped from the top surface of the mold wafer 210 and the side surfaces 218 of the vertical pit 216.

Referring the Fig. 3(f), the mold wafer 210 may then optionally be oxidized at 950° C for about six hours to grow a tip-sharpening oxidation layer 228 of silicon dioxide on the inner surfaces of the vertical pit 216 and pyramidal pit 224. At this time and temperature, the oxide at the bottom of the pit is hindered with respect to growth, and thus when a cast film is deposited in this pit, the tip sharpness can approach a 10 nm tip radius or smaller. The tip-sharpening oxidation layer 228 may have a thickness of about 3900 A.

Next, referring to Fig. 3(g), a deposition material layer 230 is then formed on the inner surfaces of the vertical pit 216 and pyramidal pit 224 and on the top surface of the mold wafer 210. The deposition material layer 230 will form the cantilever and pyramid- on-post tip. The deposition material layer 230 may, for example, be made of silicon nitride or silicon carbide. The deposition material layer 230 may have a thickness of about 400 to 1000 nm. The deposition material layer 230 is patterned and aligned such that the end of the cantilever lies over the vertical pit 216. The deposition material layer 136 may, for example, be deposited using chemical vapor deposition (CVD), sputtering, evaporation, or plating. For example, a typical low stress silicon nitride LPCVD process may use 95 seem dichlorosilane, and 200 seem ammonia, at a temperature 775° C and a pressure of 200 mTorr. Referring to Fig. 3(h), a handle wafer 232 may then optionally be bonded to the deposition material layer 230. The handle wafer 232 may, for example, be made of Pyrex or another borosilicate glass.

Finally, referring to Fig. 3(i), the mold wafer 210 is etched away using, for example, KOH, TMAH, EDP, HF/HN0₃, or XeF₂, which results in a free-standing cantilever 234 with a pyramid-on-post tip 236 extending from a bottom surface of the cantilever 234. The cantilever 234 and pyramid-on-post tip 236 are integral, both being made of the single layer of deposition material. The resulting pyramid-on-post tip 236 has an elongated post portion 238 and a pyramidal portion 240 located on the bottom of the post portion 238. Because the pyramid-on-post tip 236 and cantilever 234 are formed of a single thin layer of deposition material, the pyramid-on-post tip 236 is hollow. The width of the cantilever may be under 1000 microns, for example, about 25 microns. The length of the cantilever may also be under 1000 microns, for example, about 200 microns. The thickness of the cantilever may be between about 400 and 1000 nm, for example, about 600 nm. The pyramid-on-post tips may, for example, have a height between 5 and 20 microns and width between 3 and 10 microns.

A device with the "pyramid-on-post" tip provides several advantages over prior art devices with, for example, pyramidal tips. As with the octahedral tips, one advantage for at least some embodiments is that the height of the pyramid-on post tip is not limited by the base dimension of the square defined in the masking layer. Instead, the use of two different etching process— for example, a reactive ion etch process following by a crystallo graphic etch process— removes the previous restraints on tip height. Using the "pyramid-on-post" tip, the tip height is limited only by the depth achieved during the reactive ion etching process. The resulting mold approximately takes the form of obelisk with a height of d + 0.71w, wherein d is the depth of the pit etched by reactive ion etching, and w is the width of the opening in the masking layer.

Another advantage for at least some embodiments is that the pyramid-on-post tips have a larger surface area than typical pyramidal tips, and can therefore hold more ink than pyramidal tips, allowing for more efficient patterning of the ink onto a substrate surface. Working Examples - Octahedral Tips

Cantilevers with octahedral tips were manufactured according to the method discussed above. FIG. 6A is an SEM image showing a front, bottom perspective view of an octahedral tip attached to a triangular cantilever that was made according to one

embodiment. FIG. 6B is an SEM image showing a front, bottom perspective view of an octahedral tip attached to a triangular cantilever that was made according to one

embodiment, where the tip is slightly shorter than the tip shown in FIG. 6A. FIG. 6C is an SEM image showing a close-up side view of a side vertex of an octahedral tip that was made according to one embodiment. This side vertex can be used, for example, for imaging vertical surfaces with an atomic force microscope, or for patterning on vertical surfaces using, for example, direct write lithography.

Working Examples - Pyramid-on-Post Tips

Cantilevers with pyramid-on-post tips were manufactured according to the method discussed above. FIG. 7A is an SEM image showing a rear, side, bottom perspective view of a "pyramid-on-post" tip attached to a triangular cantilever that was made according to one embodiment. FIG. 7B is an SEM image showing a front, bottom perspective view of a "pyramid-on-post" tip attached to a triangular cantilever that was made according to one embodiment. FIG. 7C is an SEM image showing a front, bottom perspective view of a "pyramid-on-post" tip attached to a triangular cantilever that was made according to one embodiment, where a pyramid portion of the tip extends past a post portion of the tip.

Claims

WHAT IS CLAIMED IS:

1. A device comprising:

a cantilever; and

an octahedral tip extending from a bottom surface of the cantilever, wherein the octahedral tip comprises:

a top portion at which the octahedral tip is attached to the cantilever, a bottom portion comprising a first vertex, and a middle portion disposed between the top portion and the bottom portion, the middle portion comprising four additional vertices and being wider than the top portion and the bottom portion.

2. The device of claim 1, wherein the octahedral tip is integral with the cantilever.

3. The device of claim 1, wherein the cantilever and the octahedral tip are made of silicon nitride or silicon carbide.

4. The device of claim 1, wherein the cantilever and the tip are formed of a continuous layer of material having a thickness between 400 nm and 1 ,000 nm.

5. The device of claim 1, further comprising a handle wafer to which the cantilever is attached.

6. The device of claim 1 , wherein the cantilever is a part of an array of cantilevers.

7. The device of claim 1, wherein the cantilever is a part of a one-dimensional array of cantilevers.

8. The device of claim 1, wherein the cantilever is a part of a two-dimensional array of cantilevers.

9. The device of claim 1, wherein the octahedral tip has a height between 5 and 20 microns.

10. The device of claim 1, wherein the four vertices of the middle portion form a square in a plane that is parallel to the plane of the cantilever.

11. A device comprising:

a cantilever; and

a tip extending from a bottom surface of the cantilever, the tip comprising an elongated post portion and a pyramidal portion located at one end of the elongated post portion,

wherein the cantilever and the tip are formed of a continuous layer of material having a thickness between 400 nm and 1000 nm.

12. The device of claim 11, wherein the tip is integral with the cantilever.

13. The device of claim 11, wherein the cantilever and the tip are made of silicon nitride or silicon carbide.

14. The device of claim 11, wherein:

the tip is integral with the cantilever, and

the cantilever and the tip are made of silicon nitride or silicon carbide.

15. The device of claim 11, further comprising a handle wafer to which the cantilever is attached.

16. The device of claim 11, wherein the cantilever is a part of an array of cantilevers.

17. The device of claim 11, wherein the cantilever is a part of a one-dimensional array of cantilevers.

18. The device of claim 11 , wherein the cantilever is a part of a two-dimensional array of cantilevers.

19. The device of claim 11, wherein tip is a microscopic or nanoscopic tip.

20. The device of claim 11, wherein the tip has a height between 5 and 20 microns.

21. A method comprising :

providing a silicon mold wafer;

forming a vertical pit in the silicon mold wafer;

forming an octahedral pit from the vertical pit using crystallographic etching, the octahedral pit comprising

a top portion near a top surface of the silicon mold wafer,

a bottom portion comprising a first vertex, and a middle portion disposed between the top portion and the bottom portion, the middle portion comprising four additional vertices and being wider than the top portion and the bottom portion; and forming a cantilever and an octahedral tip by depositing a deposition material on a portion of the top surface of the silicon mold wafer and on an inner surface of the octahedral pit.

22. The method of claim 21, further comprising:

before forming the vertical pit, patterning a masking layer on a top surface of the silicon mold wafer; the masking layer having an opening,

wherein the vertical pit is formed on a portion of the top surface of the silicon mold wafer that corresponds to the opening.

23. The method of claim 21, further comprising, after forming the octahedral pit and before forming the cantilever and the tip, performing a tip-sharpening oxidation and patterning step.

24. The method of claim 21, wherein the step of forming the vertical pit is performed using reactive ion etching.

25. The method of claim 21, wherein the deposition material is silicon nitride or silicon carbide.

26. The method of claim 21, further comprising bonding a handle wafer to the cantilever.

27. A method comprising:

providing a silicon mold wafer;

forming a vertical pit in the silicon mold wafer;

forming an oxide layer on side and bottom surfaces of the vertical pit;

removing the oxide layer from the bottom surface of the vertical pit;

forming a pyramidal pit in the bottom surface of the vertical pit using crystallographic etching; and

forming a cantilever and a tip by depositing a deposition material on a portion of a top surface of the silicon mold wafer and on inner surfaces of the vertical pit and the pyramidal pit.

28. The method of claim 27, further comprising:

29. The method of claim 27, further comprising, after forming the pyramidal pit and before forming the cantilever and the tip, performing a tip-sharpening oxidation and patterning step.

30. The method of claim 27, wherein the step of forming the vertical pit is performed using reactive ion etching.

31. The method of claim 27, wherein the deposition material is silicon nitride or silicon carbide.

32. The method of claim 27, further comprising bonding a handle wafer to the cantilever.

33. A method comprising :

providing a device comprising:

a cantilever; and

a top portion at which the octahedral tip is attached to the cantilever,

a bottom portion comprising a first vertex, and

a middle portion disposed between the top portion and the bottom portion, the middle portion comprising four additional vertices and being wider than the top portion and the bottom portion; and

transferring an ink or patterning compound from the octahedral tip to a substrate surface.

34. A method comprising:

providing a device comprising:

a cantilever; and

wherein the cantilever and the tip are formed of a continuous layer of material having a thickness between 400 nm and 1000 nm; and

transferring an ink or patterning compound from the tip to a substrate surface.