WO2021059009A1 - Fabrication of an atomic force microscope probe - Google Patents

Fabrication of an atomic force microscope probe Download PDF

Info

Publication number
WO2021059009A1
WO2021059009A1 PCT/IB2019/058268 IB2019058268W WO2021059009A1 WO 2021059009 A1 WO2021059009 A1 WO 2021059009A1 IB 2019058268 W IB2019058268 W IB 2019058268W WO 2021059009 A1 WO2021059009 A1 WO 2021059009A1
Authority
WO
WIPO (PCT)
Prior art keywords
layer
substrate
silicon oxide
oxide layer
etching
Prior art date
Application number
PCT/IB2019/058268
Other languages
French (fr)
Inventor
Milad GHAROONI
Reza Ramezani
Hamed ABIRI
Golfam SADEGHIAN
Original Assignee
Gharooni Milad
Reza Ramezani
Abiri Hamed
Sadeghian Golfam
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Gharooni Milad, Reza Ramezani, Abiri Hamed, Sadeghian Golfam filed Critical Gharooni Milad
Priority to PCT/IB2019/058268 priority Critical patent/WO2021059009A1/en
Publication of WO2021059009A1 publication Critical patent/WO2021059009A1/en

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
    • G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
    • G01Q60/24—AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
    • G01Q60/38—Probes, their manufacture, or their related instrumentation, e.g. holders

Definitions

  • the present disclosure relates to atomic force microscopy (AFM), particularly relates to methods for fabricating AFM probes, and more particularly relates to methods for fabricating silicon cantilevers with integrated silicon tips of AFM probes.
  • AFM atomic force microscopy
  • Atomic force microscopy is usually used for monitoring, visualizing and characterizing micro and nanostructures. This characterization is accompanied by a sensitive sensor that may include a support element that holds a micro cantilever. The force between a sample and a tip at the end of the micro cantilever actuates the micro cantilever and bends it. The deflection of the micro cantilever leads to a change in a laser position on a photodetector.
  • Atomic force microscopy has become an appointed technique for surface analysis that permits imaging of surface topographies with a resolution of a few nanometers, even down to atomic ranges.
  • the core element of this technology is the scanning probe. The quality of the probes contributes to the resolution of the surface analysis.
  • AFM sensors that are based on micromachining silicon.
  • a challenge in the fabrication process is controlling the thickness of the cantilever as an essential parameter that affects the resonance frequency.
  • Many processes have been presented for introducing a repeatable solution to control the thickness of cantilever.
  • Another parameter that impacts AFM imaging is the roughness of the backside surface of the cantilever on which the laser beam is focused.
  • An exemplary method may include forming a handle layer on a backside of a substrate, where the substrate may include a silicon wafer with a first front silicon oxide layer grown on a front side of the silicon wafer and a first back silicon oxide layer grown on the backside of the silicon wafer.
  • the substrate may further include a front silicon nitrate layer deposited on the first front silicon oxide layer and a back silicon nitride layer deposited on the first back silicon oxide layer.
  • An atomic force microscope probe may be fabricated by further forming an AFM tip on the front side of the substrate, and forming an AFM cantilever integrated with the AFM tip.
  • Forming the AFM cantilever may include growing a second front silicon oxide layer on the front side of the substrate, the second front silicon oxide layer covering the front side and the formed AFM tip, growing a second back silicon oxide layer on the substrate, the second back silicon oxide layer covering a lower surface of the handle layer, transferring a pattern of the AFM cantilever to the front side of the substrate by a photolithographic method, etching the second front silicon oxide layer utilizing the pattern of the AFM cantilever, and etching the silicon wafer from the front side to form the AFM cantilever.
  • an exemplary method for fabricating an atomic force microscope probe may further include etching remainder of the second front silicon oxide layer and the second back silicon oxide layer.
  • growing a second front silicon oxide layer on the substrate and growing a second back silicon oxide layer on the substrate may be performed simultaneously by placing the substrate with the handle layer and the AFM tip formed thereon in an oxidation furnace at a temperature between 1050 °C and 1100 °C under oxygen flow.
  • etching the second front silicon oxide layer utilizing the pattern of the AFM cantilever may include wet etching portions of second front silicon oxide layer not covered by the pattern of the AFM cantilever by a buffered HF solution.
  • etching the silicon layer from the front side to form the AFM cantilever may include etching the silicon layer utilizing a KOH solution at a temperature between 60 °C and 80 °C.
  • forming the AFM tip on the front side of the substrate may include transferring a pattern of the AFM tip to the front side of the substrate by a photolithographic method, etching the first front silicon oxide layer and the front silicon nitrate layer utilizing the pattern of the AFM tip, and etching the silicon wafer from the front side to form the AFM tip.
  • etching the first front silicon oxide layer and the front silicon nitrate layer utilizing the pattern of the AFM tip may include etching a portion of the front silicon nitrate layer not covered by the pattern of the AFM tip by a reactive plasma etchant, and wet etching portions of the first front silicon oxide layer not covered by the pattern of the AFM tip by a buffered HF solution.
  • forming the handle layer may include transferring a location of a handle window to the backside of the substrate by a photolithographic method, etching the first back silicon oxide layer and the back silicon nitrate layer at the location of the handle window, and etching the handle layer within the silicon layer.
  • FIG. 1A illustrates a substrate utilized for fabricating an AFM probe, consistent with one or more exemplary embodiments of the present disclosure
  • FIG. IB illustrates a substrate with a handle window opened on a first back silicon oxide layer and a back silicon nitride layer thereof, consistent with one or more exemplary embodiments of the present disclosure
  • FIG. 1C illustrates a substrate with a handle layer etched into an Si layer thereof, consistent with one or more exemplary embodiments of the present disclosure
  • FIG. ID illustrates a substrate with its first front silicon oxide layer and front silicon nitride layer etched based on the pattern of AFM tip transferred thereto by a photolithography method, consistent with one or more exemplary embodiments of the present disclosure
  • FIG. IE illustrates a substrate with an AFM tip formed on an Si layer thereof, consistent with one or more exemplary embodiments of the present disclosure
  • FIG. IF illustrates a substrate with a second front silicon oxide layer and a second back silicon oxide layer grown thereon, consistent with one or more exemplary embodiment of the present disclosure
  • FIG. 1G illustrates a substrate with its second front silicon oxide layer etched based on the pattern of AFM cantilever transferred thereto by a photolithography method, consistent with one or more exemplary embodiments of the present disclosure
  • FIG. 1H illustrates a substrate with an AFM cantilever formed on an Si layer thereof, consistent with one or more exemplary embodiments of the present disclosure
  • FIG. II illustrates a substrate with a handle layer, an AFM cantilever, and an AFM tip formed thereon, consistent with one or more exemplary embodiments of the present disclosure
  • FIG. 2A illustrates a flowchart of a method of fabricating an AFM probe, consistent with one or more exemplary embodiments of the present disclosure
  • FIG. 2B illustrates a flowchart for performing a step of forming a handle layer on a backside of a substrate, consistent with one or more exemplary embodiments of the present disclosure
  • FIG. 2C illustrates a flowchart for performing a step of forming an AFM tip on a front side of a substrate, consistent with one or more exemplary embodiments of the present disclosure
  • FIG. 2D illustrates a flowchart for performing a step of forming an AFM cantilever on a front side of a substrate, consistent with one or more exemplary embodiments of the present disclosure.
  • the present disclosure is directed to exemplary methods for fabricating atomic force microscope (AFM) probes with silicon cantilevers integrally formed with silicon tips.
  • An exemplary method for fabricating an AFM probe may include steps of forming a handle layer on a backside of a silicon wafer (substrate), forming an AFM tip on a front side of the substrate, and forming an AFM cantilever integrated with the formed AFM tip.
  • An exemplary method for fabricating an AFM probe may include growing silicon oxide layers on the front and back sides of a silicon substrate after forming an AFM tip on front side of the substrate and before forming an AFM cantilever on the substrate.
  • such addition of silicon oxide layers may allow for forming an AFM cantilever with better control over the cantilever thickness while maintaining the smoothness of a back surface of the cantilever during later etching steps.
  • AFM atomic force microscope
  • FIG. 1A illustrates a substrate 10 utilized for fabricating an AFM probe, consistent with one or more exemplary embodiments of the present disclosure.
  • substrate 10 may include a silicon (Si) layer 102, silicon oxide layers (104a, 104b), and silicon nitride layers (106a, 106b).
  • preparation of substrate 10 may include growing a first front silicon oxide layer 104a on a front side of Si layer 102 and a first back silicon oxide layer 104b on a backside of Si layer 102 by thermal oxidation at a temperature between 800 °C and 1200 °C.
  • thermal oxidation of Si layer 102 may be performed by either wet oxidation using water vapor as an oxidant or dry oxidation using molecular oxygen as the oxidant.
  • Si layer 102 may be an ⁇ 100> N-type silicon wafer with a thickness of 350 ⁇ 10 nm and thermal oxidation of Si layer 102 may be performed in an oxidation furnace at a temperature between 1050 °C and 1100 °C under oxygen flow for a period of approximately 2 hours to grow silicon oxide layers on front and back sides of Si layer 102 with thicknesses of approximately 120+20 nm.
  • Si layer 102 may be a silicon wafer with a resistance of 0.01 to 0.001 Qm that may include trace amounts of dopants such as antimony or phosphorus in the ppm range.
  • Si layer 102 may include other common dopants known in the art or may include no dopants.
  • preparation of substrate 10 may further include depositing a front silicon nitride layer 106a on first front silicon oxide layer 104a and a back silicon nitride layer 106b on first back silicon oxide layer 104b by a plasma-enhanced chemical vapor deposition (PECVD) method.
  • PECVD plasma-enhanced chemical vapor deposition
  • Silane (SitF) and ammonia (NH3) gasses may be utilized as reactants in a PECVD method for depositing front silicon nitride layer 106a and back silicon nitride layer 106b.
  • front silicon nitride layer 106a may be deposited on first front silicon oxide layer 104a
  • back silicon nitride layer 106b may be deposited on first back silicon oxide layer 104b with thicknesses of approximately 300+20 nm.
  • deposition of front silicon nitride layer 106a and back silicon nitride layer 106b may be performed in a low-pressure chemical vapor deposition (LPCVD) furnace at temperatures of approximately 700 °C to 850 °C.
  • LPCVD low-pressure chemical vapor deposition
  • substrate 10 may be either a double-side polished substrate or a single-side polished substrate.
  • a double-side polish may be performed on substrate 10 to flatten front and back sides of substrate 10, or a single-side polish may be performed on substrate 10 to flatten front side of substrate 10.
  • FIG. 2A illustrates a flowchart of a method 20 of fabricating an AFM probe, consistent with one or more exemplary embodiments of the present disclosure.
  • method 20 may include a step 22 of forming a handle layer on a backside of a substrate, a step 24 of forming an AFM tip on a front side of the substrate, and a step 26 of forming an AFM cantilever integrated with the AFM tip.
  • FIG. 2B illustrates a flowchart for performing step 22 of forming a handle layer on a backside of a substrate, consistent with one or more exemplary embodiments of the present disclosure.
  • the substrate may be a substrate similar to substrate 10, which may include Si layer 102 with first front silicon oxide layer 104a and first back silicon oxide layer 104b grown on Si layer 102 and front silicon nitride layer 106a and back silicon nitride layer 106b deposited on silicon oxide layers (104a and 104b).
  • step 22 of forming a handle layer on a backside of a substrate may include a step 220 of transferring a location of a handle window to the backside of the substrate by a photolithographic method and a step 222 of etching a first back silicon oxide layer and a back silicon nitride layer at the location of the handle window.
  • FIG. IB illustrates substrate 10 with a handle window 108 opened on first back silicon oxide layer 104a and back silicon nitride layer 106b thereof, consistent with one or more exemplary embodiments of the present disclosure.
  • step 220 of transferring a location of a handle window to the backside of the substrate by a photolithographic method may include forming a photoresist mask on the backside of substrate 10 and baking substrate 10 to solidify the photoresist mask for creating a more durable mask for performing later etching steps.
  • substrate 10 may first be washed utilizing acetone and deionized water, and then substrate 10 may be dried with nitrogen. After that, a layer of a photoresist such as Shipley 1813 may be coated onto the substrate 10 utilizing a spin coater. Then, the coated photoresist may be pre-baked at a temperature of approximately 90 °C for approximately 1 minute.
  • a chrome mask with a pattern defining the location of handle window 108 may be placed on the backside of substrate 10 by a hard contact method, and then the backside may be exposed to an intense light with an intensity of approximately 1300 W/cm 3 and a wavelength of approximately 405 nm. After that, substrate 10 may be placed inside a standard developer solution for approximately 25 seconds, and then substrate 10 may be rinsed and dried. In the next step, substrate 10 may be baked at 120 °C for approximately 2 minutes.
  • step 222 of etching a first back silicon oxide layer and a back silicon nitride layer at the location of the handle window may include etching a portion of the backside of the substrate not covered by the photoresist mask. This portion of the backside of the substrate not covered by the photoresist mask was referred to as the handle window in preceding paragraphs.
  • back silicon nitride layer 106b may be etched by an etching method such as a reactive ion etching method, where a chemically reactive plasma such as SF 6 plasma may be used to remove a portion of back silicon nitride layer 106b not covered by the photoresist mask at the location of handle window 108.
  • a reactive ion etching method may be performed on substrate 10, where a 165 seem SF 6 gas flow at 250 W may be utilized for patterning back silicon nitride layer 106b for approximately 380 seconds. After etching back silicon nitride layer 106b at the location of handle window 108, the photoresist layer may be washed with acetone and then substrate 10 may be rinsed and dried.
  • buffered HF wet etching may be used to etch first back silicon oxide layer 104b at the location of handle window 108.
  • first back silicon oxide layer 104b may be etched by buffered HF solution with a concentration of approximately 10 wt. %.
  • buffered HF wet etching may be performed on substrate 10 by placing substrate 10 inside a buffered HF solution that may include HF and a 40 wt. % ammonium fluoride (NH 4 F) solution with a weight ratio of approximately 3:1 (HF: NH 4 F) for approximately 30 seconds. Then, substrate 10 may be rinsed and dried.
  • Si layer 102 may be exposed at the location of handle window 108 for later etching steps for forming the handle layer.
  • step 22 of forming a handle layer on a backside of a substrate may further include a step 224 of etching the handle layer within the Si layer through the handle window.
  • FIG. 1C illustrates substrate 10 with a handle layer 110 etched into Si layer 102 thereof, consistent with one or more exemplary embodiments of the present disclosure.
  • KOH solution may be utilized for etching handle layer 110 into Si layer 102. It should be understood that other etching agents may similarly be used for etching handle layer 110 into Si layer 102.
  • the backside of substrate 10 may be exposed to an etching solution including KOH at a temperature of approximately 60 °C to 80 °C.
  • a wet etching bath may be prepared that may include KOH and isopropyl alcohol and then substrate 10 may be placed within the wet etching bath such that the backside of substrate 10 may be exposed to the wet etching solution.
  • the wet etching solution within the wet etching bath may include KOH with a concentration of about 25 wt.% and isopropyl alcohol with a concentration of about 12.5 wt.%.
  • adding isopropyl alcohol to the wet etching solution may allow for etching handle layer 110 with smooth edges.
  • handle layer 110 may be etched into Si layer 102 by exposing the backside of substrate 10 to the wet etching solution at a temperature of approximately 65 °C for approximately 12 hours under stirring. In an exemplary embodiment, etching handle layer 110 into Si layer 102 may be carried out until a thickness 112 of Si layer not etched above handle window 108 may be approximately 20 pm. In an exemplary embodiment, after etching handle layer 110 into Si layer 102, substrate 10 may be rinsed and dried.
  • FIG. 2C illustrates a flowchart for performing step 24 of forming an AFM tip on the front side of a substrate, consistent with one or more exemplary embodiments of the present disclosure.
  • step 24 of forming an AFM tip on a front side of a substrate may include a step 240 of transferring a pattern of the AFM tip to the front side of the substrate by a photolithographic method and a step 242 of etching a first front silicon oxide layer and a front silicon nitride layer utilizing the pattern of the AFM tip.
  • step 240 of transferring a pattern of the AFM tip to the front side of the substrate by a photolithographic method may include forming a photoresist mask on the front side of substrate 10 and baking substrate 10 to solidify the photoresist mask for creating a more durable mask for performing later etching steps.
  • substrate 10 may first be washed utilizing acetone and deionized water, and then substrate 10 may be dried with nitrogen. After that, a layer of a photoresist such as Shipley 1813 may be coated onto the substrate 10 utilizing a spin coater. Then, the coated photoresist may be pre-baked at a temperature of approximately 90 °C for approximately 1 minute.
  • a chrome mask with a pattern defining the location of the AFM tip may be placed on the front side of substrate 10 by a hard contact method, and then the front side may be exposed to an intense light with an intensity of approximately 1300 W/cm 3 and a wavelength of approximately 405 nm. After that, substrate 10 may be placed inside a standard developer solution for approximately 25 seconds, and then substrate 10 may be rinsed and dried. In the next step, substrate 10 may be baked at 120 °C for approximately 2 minutes.
  • step 242 of etching a first front silicon oxide layer and a front silicon nitride layer utilizing the pattern of the AFM tip may include etching a portion of the front side of the substrate not covered by the photoresist mask.
  • FIG. ID illustrates substrate 10 with its first front silicon oxide layer 104a and front silicon nitride layer 106a etched based on the pattern of AFM tip transferred thereto by a photolithography method, consistent with one or more exemplary embodiments of the present disclosure.
  • front silicon nitride layer 106a may be etched by an etching method such as a reactive ion etching method, where a chemically reactive plasma such as SF 6 plasma may be used to remove a portion of front silicon nitride layer 106a not covered by the photoresist mask.
  • a reactive ion etching method may be performed on substrate 10, where a 165 seem SF 6 gas flow at 250 W may be utilized for patterning front silicon nitride layer 106a for approximately 380 seconds.
  • buffered HF wet etching may be used to etch first front silicon oxide layer 104a.
  • first front silicon oxide layer 104a may be etched by buffered HF solution with a concentration of approximately 10 wt. %.
  • buffered HF wet etching may be performed on substrate 10 by placing substrate 10 inside a buffered HF solution that may include HF and a 40 wt. % ammonium fluoride (NH 4 F) solution with a weight ratio of approximately 3:1 (HF: NH 4 F) for approximately 30 seconds. Then, substrate 10 may be rinsed and dried.
  • a buffered HF solution that may include HF and a 40 wt. % ammonium fluoride (NH 4 F) solution with a weight ratio of approximately 3:1 (HF: NH 4 F) for approximately 30 seconds.
  • Si layer 102 may be exposed except for the location of the AFM tip which is covered by the remaining portions of front silicon nitride layer 106a and first front silicon oxide layer 104a. After that, the photoresist layer may be washed with acetone, and then substrate 10 may be rinsed and dried.
  • step 24 of forming an AFM tip on a front side of a substrate may further include a step 244 of etching the Si layer from the front side of the substrate to form the AFM tip.
  • FIG. IE illustrates substrate 10 with an AFM tip 114 formed on Si layer 102 thereof, consistent with one or more exemplary embodiments of the present disclosure.
  • KOH solution may be utilized for etching Si layer 102 to form AFM tip 114. It should be understood that other etching agents may similarly be used for etching Si layer 102.
  • the front side of substrate 10 may be exposed to an etching solution, including KOH at a temperature of approximately 60 °C to 80 °C.
  • a wet etching bath may be prepared that may include KOH and isopropyl alcohol and then substrate 10 may be placed within the wet etching bath such that the front side of substrate 10 may be exposed to the wet etching solution.
  • the wet etching solution within the wet etching bath may include KOH with a concentration of about 25 wt.% and isopropyl alcohol with a concentration of about 12.5 wt.%.
  • adding isopropyl alcohol to the wet etching solution may allow for etching AFM tip 114 with smooth edges.
  • AFM tip 114 may be formed on Si layer 102 by exposing the front side of substrate 10 to the wet etching solution at a temperature of approximately 65 °C for approximately 12 hours under stirring. In an exemplary embodiment, after forming AFM tip 114 on Si layer 102, substrate 10 may be rinsed and dried. [0047] Referring back to FIG. 2A, in an exemplary embodiment, after performing step 22 of forming the handle layer on the backside of the substrate and step 24 of forming the AFM tip on the front side of the substrate, method 20 may proceed to step 26 of forming an AFM cantilever integrated with the AFM tip.
  • FIG. 2D illustrates a flowchart for performing step 26 of forming an AFM cantilever on a front side of a substrate, consistent with one or more exemplary embodiments of the present disclosure.
  • step 26 of forming the AFM cantilever on the front side of the substrate may include a step 260 of growing a second front silicon oxide layer on the front side of the substrate, a step 262 of growing a second back silicon oxide layer on the backside of the substrate, a step 264 of transferring a pattern of the AFM cantilever to the front side of the substrate by a photolithographic method, a step 266 of etching the second front oxide layer utilizing the pattern of the AFM cantilever, and a step 268 of etching the Si layer from the front side to form the AFM cantilever.
  • step 260 of growing a second front silicon oxide layer on the front side of the substrate and step 262 of growing a second back silicon oxide layer on the backside of the substrate may be performed simultaneously by placing the substrate with the handle layer and the AFM tip formed thereon in an oxidation furnace at a temperature between approximately 1050 °C and 1100 °C under an agent flow, such as oxygen flow.
  • substrate 10 as shown in FIG. IE with handle layer 110 and AFM tip 114 formed thereon may be placed in an oxidation furnace under a 25 seem oxygen flow at a temperature of approximately 1050 °C for about 90 minutes to form a second front silicon oxide layer and a second back silicon oxide layer thereon with thicknesses of approximately 200 to 300 nm.
  • FIG. IF illustrates substrate 10 with a second front silicon oxide layer 116a and a second back silicon oxide layer 116b grown thereon, consistent with one or more exemplary embodiment of the present disclosure.
  • second front silicon oxide layer 116a may cover the front side of substrate 10, including a top surface of AFM tip 114.
  • second back silicon oxide layer 116b may cover a lower surface of handle layer 110.
  • the method may proceed to step 264 of transferring a pattern of the AFM cantilever to the front side of the substrate by a photolithographic method.
  • step 264 of transferring the pattern of the AFM cantilever to the front side of the substrate by a photolithographic method may include forming a photoresist mask on the front side of substrate 10 and baking substrate 10 to solidify the photoresist mask for creating a more durable mask for performing later etching steps.
  • substrate 10 may first be washed utilizing acetone and deionized water, and then substrate 10 may be dried with nitrogen. After that, a layer of a photoresist such as Shipley 1813 may be coated onto the substrate 10 utilizing a spin coater. Then, the coated photoresist may be pre-baked at a temperature of approximately 90 °C for approximately 1 minute.
  • a chrome mask with a pattern defining the location of the AFM cantilever may be placed on the front side of substrate 10 by a hard contact method, and then the front side may be exposed to an intense light with an intensity of approximately 1300 W/cm 3 and a wavelength of approximately 405 nm. After that, substrate 10 may be placed inside a standard developer solution for approximately 25 seconds, and then substrate 10 may be rinsed and dried. In the next step, substrate 10 may be baked at 120 °C for approximately 2 minutes.
  • step 266 of etching a second front silicon oxide layer utilizing the pattern of the AFM cantilever may include etching a portion of the front side of the substrate not covered by the photoresist mask.
  • FIG. 1G illustrates substrate 10 with its second front silicon oxide layer 116a etched based on the pattern of AFM cantilever transferred thereto by a photolithography method, consistent with one or more exemplary embodiments of the present disclosure.
  • buffered HF wet etching may be used to etch second front silicon oxide layer 116a.
  • second front silicon oxide layer 116a may be etched by buffered HF solution with a concentration of approximately 10 wt. %.
  • buffered HF wet etching may be performed on substrate 10 by placing substrate 10 inside a buffered HF solution that may include HF and a 40 wt. % ammonium fluoride (NH4F) solution with a weight ratio of approximately 3:1 (HF: NH4F) for approximately 30 seconds. Then, substrate 10 may be rinsed and dried.
  • a buffered HF solution that may include HF and a 40 wt. % ammonium fluoride (NH4F) solution with a weight ratio of approximately 3:1 (HF: NH4F) for approximately 30 seconds.
  • the method may proceed to step 268 of etching the Si layer from the front side to form the AFM cantilever.
  • FIG. 1H illustrates substrate 10 with an AFM cantilever 118 formed on Si layer 102 thereof, consistent with one or more exemplary embodiments of the present disclosure.
  • KOH solution may be utilized for etching Si layer 102 to form AFM cantilever 118. It should be understood that other etching agents may similarly be used for etching Si layer 102.
  • the front side of substrate 10 may be exposed to an etching solution including KOH at a temperature of approximately 60 °C to 80 °C.
  • a wet etching bath may be prepared that may include KOH and isopropyl alcohol and then substrate 10 may be placed within the wet etching bath such that the front side of substrate 10 may be exposed to the wet etching solution.
  • the wet etching solution within the wet etching bath may include KOH with a concentration of about 25 wt.% and isopropyl alcohol with a concentration of about 12.5 wt.%.
  • adding isopropyl alcohol to the wet etching solution may allow for etching AFM cantilever 118 with smooth edges.
  • AFM cantilever 118 may be formed on Si layer 102 by exposing the front side of substrate 10 to the wet etching solution at a temperature of approximately 65 °C for a period of approximately 12 hours under stirring. [0056] In an exemplary embodiment, after forming AFM cantilever 118 on Si layer 102, second front silicon oxide layer 116a and second back silicon oxide layer 116b may be etched by buffered HF as was described in the preceding paragraphs.
  • FIG. II illustrates substrate 10 with handle layer 110, AFM cantilever 118, and AFM tip 114 formed thereon, consistent with one or more exemplary embodiments of the present disclosure. Referring to FIG.
  • AFM cantilever may be integrally formed with AFM tip 114 as was described.
  • growing second back silicon oxide layer 116b in step 262 may allow for better control over the thickness of AFM cantilever 118 during step 266, since etching process of Si layer 102 from a front side of substrate 10 may continue down to second back silicon oxide layer 116b.
  • growing second back silicon oxide layer 116b may allow for maintaining the smoothness of a lower surface (designated by reference numeral 119 in FIG. II) of AFM cantilever 118 while Si layer 102 is being etched by KOH to form AFM cantilever 118 in step 266.
  • Exemplary methods of the present disclosure may allow for forming an AFM cantilever with better control over the cantilever thickness while maintaining the smoothness of a back surface of the cantilever during etching steps. Maintaining the smoothness of a back surface of the cantilever by the extra second back silicon oxide layer grown on the substrate after forming the tip and before forming the cantilever may have a considerable effect on reducing the roughness of the back surface of the cantilever and improving the reflective properties of the back surface of the cantilever.

Landscapes

  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Weting (AREA)

Abstract

An atomic force microscope probe may be fabricated by forming a handle layer on a backside of a substrate, where the substrate may include a silicon wafer with a first front silicon oxide layer grown on a front side of the silicon wafer and a first back silicon oxide layer grown on the backside of silicon wafer. The substrate may further include a front silicon nitrate layer deposited on the first front silicon oxide layer and a back silicon nitride layer deposited on the first back silicon oxide layer. An atomic force microscope probe may be fabricated by further forming an AFM tip on the front side of the substrate, and forming an AFM cantilever integrated with the AFM tip. Forming the AFM cantilever may include growing a second front silicon oxide layer on the front side of the substrate, the second front silicon oxide layer covering the front side and the formed AFM tip, growing a second back silicon oxide layer on the substrate, the second back silicon oxide layer covering a lower surface of the handle layer, transferring a pattern of the AFM cantilever to the front side of the substrate by a photolithographic method, etching the second front silicon oxide layer utilizing the pattern of the AFM cantilever, and etching the silicon wafer from the front side to form the AFM cantilever.

Description

FABRICATION OF AN ATOMIC FORCE MICROSCOPE PROBE
TECHNICAL FIELD
[0001] The present disclosure relates to atomic force microscopy (AFM), particularly relates to methods for fabricating AFM probes, and more particularly relates to methods for fabricating silicon cantilevers with integrated silicon tips of AFM probes.
BACKGROUND ART
[0002] Atomic force microscopy (AFM) is usually used for monitoring, visualizing and characterizing micro and nanostructures. This characterization is accompanied by a sensitive sensor that may include a support element that holds a micro cantilever. The force between a sample and a tip at the end of the micro cantilever actuates the micro cantilever and bends it. The deflection of the micro cantilever leads to a change in a laser position on a photodetector. Atomic force microscopy has become an appointed technique for surface analysis that permits imaging of surface topographies with a resolution of a few nanometers, even down to atomic ranges. The core element of this technology is the scanning probe. The quality of the probes contributes to the resolution of the surface analysis.
[0003] Different processes have been investigated for manufacturing AFM sensors that are based on micromachining silicon. A challenge in the fabrication process is controlling the thickness of the cantilever as an essential parameter that affects the resonance frequency. Many processes have been presented for introducing a repeatable solution to control the thickness of cantilever. Another parameter that impacts AFM imaging is the roughness of the backside surface of the cantilever on which the laser beam is focused.
[0004] There is, therefore, a need for a method of fabricating an AFM probe that may allow for better control over the thickness of the formed cantilever and maintaining the smoothness of the backside surface of the cantilever during the fabrication process.
SUMMARY OF THE DISCLOSURE
[0005] This summary is intended to provide an overview of the subject matter of the present disclosure, and is not intended to identify essential elements or key elements of the subject matter, nor is it intended to be used to determine the scope of the claimed implementations. The proper scope of the present disclosure may be ascertained from the claims set forth below in view of the detailed description below and the drawings.
[0006] According to one or more exemplary embodiments, the present disclosure is directed to an exemplary method for fabricating an atomic force microscope probe. An exemplary method may include forming a handle layer on a backside of a substrate, where the substrate may include a silicon wafer with a first front silicon oxide layer grown on a front side of the silicon wafer and a first back silicon oxide layer grown on the backside of the silicon wafer. The substrate may further include a front silicon nitrate layer deposited on the first front silicon oxide layer and a back silicon nitride layer deposited on the first back silicon oxide layer. An atomic force microscope probe may be fabricated by further forming an AFM tip on the front side of the substrate, and forming an AFM cantilever integrated with the AFM tip. Forming the AFM cantilever may include growing a second front silicon oxide layer on the front side of the substrate, the second front silicon oxide layer covering the front side and the formed AFM tip, growing a second back silicon oxide layer on the substrate, the second back silicon oxide layer covering a lower surface of the handle layer, transferring a pattern of the AFM cantilever to the front side of the substrate by a photolithographic method, etching the second front silicon oxide layer utilizing the pattern of the AFM cantilever, and etching the silicon wafer from the front side to form the AFM cantilever.
[0007] In an exemplary embodiment, an exemplary method for fabricating an atomic force microscope probe may further include etching remainder of the second front silicon oxide layer and the second back silicon oxide layer.
[0008] In an exemplary embodiment, growing a second front silicon oxide layer on the substrate and growing a second back silicon oxide layer on the substrate may be performed simultaneously by placing the substrate with the handle layer and the AFM tip formed thereon in an oxidation furnace at a temperature between 1050 °C and 1100 °C under oxygen flow. [0009] In an exemplary embodiment, etching the second front silicon oxide layer utilizing the pattern of the AFM cantilever may include wet etching portions of second front silicon oxide layer not covered by the pattern of the AFM cantilever by a buffered HF solution.
[00010] In an exemplary embodiment, etching the silicon layer from the front side to form the AFM cantilever may include etching the silicon layer utilizing a KOH solution at a temperature between 60 °C and 80 °C. [0010] In an exemplary embodiment, forming the AFM tip on the front side of the substrate may include transferring a pattern of the AFM tip to the front side of the substrate by a photolithographic method, etching the first front silicon oxide layer and the front silicon nitrate layer utilizing the pattern of the AFM tip, and etching the silicon wafer from the front side to form the AFM tip.
[0011] In an exemplary embodiment, etching the first front silicon oxide layer and the front silicon nitrate layer utilizing the pattern of the AFM tip may include etching a portion of the front silicon nitrate layer not covered by the pattern of the AFM tip by a reactive plasma etchant, and wet etching portions of the first front silicon oxide layer not covered by the pattern of the AFM tip by a buffered HF solution.
[0012] In an exemplary embodiment, forming the handle layer may include transferring a location of a handle window to the backside of the substrate by a photolithographic method, etching the first back silicon oxide layer and the back silicon nitrate layer at the location of the handle window, and etching the handle layer within the silicon layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The drawing figures depict one or more implementations in accord with the present teachings, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements.
[0014] FIG. 1A illustrates a substrate utilized for fabricating an AFM probe, consistent with one or more exemplary embodiments of the present disclosure;
[0015] FIG. IB illustrates a substrate with a handle window opened on a first back silicon oxide layer and a back silicon nitride layer thereof, consistent with one or more exemplary embodiments of the present disclosure;
[0016] FIG. 1C illustrates a substrate with a handle layer etched into an Si layer thereof, consistent with one or more exemplary embodiments of the present disclosure;
[0017] FIG. ID illustrates a substrate with its first front silicon oxide layer and front silicon nitride layer etched based on the pattern of AFM tip transferred thereto by a photolithography method, consistent with one or more exemplary embodiments of the present disclosure;
[0018] FIG. IE illustrates a substrate with an AFM tip formed on an Si layer thereof, consistent with one or more exemplary embodiments of the present disclosure; [0019] FIG. IF illustrates a substrate with a second front silicon oxide layer and a second back silicon oxide layer grown thereon, consistent with one or more exemplary embodiment of the present disclosure;
[0020] FIG. 1G illustrates a substrate with its second front silicon oxide layer etched based on the pattern of AFM cantilever transferred thereto by a photolithography method, consistent with one or more exemplary embodiments of the present disclosure;
[0021] FIG. 1H illustrates a substrate with an AFM cantilever formed on an Si layer thereof, consistent with one or more exemplary embodiments of the present disclosure [0022] FIG. II illustrates a substrate with a handle layer, an AFM cantilever, and an AFM tip formed thereon, consistent with one or more exemplary embodiments of the present disclosure; [0023] FIG. 2A illustrates a flowchart of a method of fabricating an AFM probe, consistent with one or more exemplary embodiments of the present disclosure;
[0024] FIG. 2B illustrates a flowchart for performing a step of forming a handle layer on a backside of a substrate, consistent with one or more exemplary embodiments of the present disclosure;
[0025] FIG. 2C illustrates a flowchart for performing a step of forming an AFM tip on a front side of a substrate, consistent with one or more exemplary embodiments of the present disclosure; and
[0026] FIG. 2D illustrates a flowchart for performing a step of forming an AFM cantilever on a front side of a substrate, consistent with one or more exemplary embodiments of the present disclosure.
DESCRIPTION OF EMBODIMENTS
[0027] In the following detailed description, numerous specific details are set forth by way of examples to provide a thorough understanding of the relevant teachings related to the exemplary embodiments. However, it should be apparent that the present teachings may be practiced without such details. In other instances, well-known methods, procedures, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings.
[0028] The following detailed description is presented to enable a person skilled in the art to make and use the methods and devices disclosed in exemplary embodiments of the present disclosure. For purposes of explanation, specific nomenclature is set forth to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that these specific details are not required to practice the disclosed exemplary embodiments. Descriptions of specific exemplary embodiments are provided only as representative examples. Various modifications to the exemplary implementations will be plain to one skilled in the art, and the general principles defined herein may be applied to other implementations and applications without departing from the scope of the present disclosure. The present disclosure is not intended to be limited to the implementations shown but is to be accorded the broadest possible scope consistent with the principles and features disclosed herein.
[0029] The present disclosure is directed to exemplary methods for fabricating atomic force microscope (AFM) probes with silicon cantilevers integrally formed with silicon tips. An exemplary method for fabricating an AFM probe may include steps of forming a handle layer on a backside of a silicon wafer (substrate), forming an AFM tip on a front side of the substrate, and forming an AFM cantilever integrated with the formed AFM tip. An exemplary method for fabricating an AFM probe may include growing silicon oxide layers on the front and back sides of a silicon substrate after forming an AFM tip on front side of the substrate and before forming an AFM cantilever on the substrate. In exemplary embodiments, such addition of silicon oxide layers may allow for forming an AFM cantilever with better control over the cantilever thickness while maintaining the smoothness of a back surface of the cantilever during later etching steps. To better understand the exemplary methods disclosed herein for the fabrication of an AFM probe, schematic fabrication steps for an atomic force microscope (AFM) probe are illustrated in FIGs. 1A-I, consistent with one or more exemplary embodiments of the present disclosure.
[0030] FIG. 1A illustrates a substrate 10 utilized for fabricating an AFM probe, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, substrate 10 may include a silicon (Si) layer 102, silicon oxide layers (104a, 104b), and silicon nitride layers (106a, 106b). In an exemplary embodiment, preparation of substrate 10 may include growing a first front silicon oxide layer 104a on a front side of Si layer 102 and a first back silicon oxide layer 104b on a backside of Si layer 102 by thermal oxidation at a temperature between 800 °C and 1200 °C. In exemplary embodiments, thermal oxidation of Si layer 102 may be performed by either wet oxidation using water vapor as an oxidant or dry oxidation using molecular oxygen as the oxidant. In an exemplary embodiment, Si layer 102 may be an <100> N-type silicon wafer with a thickness of 350 ± 10 nm and thermal oxidation of Si layer 102 may be performed in an oxidation furnace at a temperature between 1050 °C and 1100 °C under oxygen flow for a period of approximately 2 hours to grow silicon oxide layers on front and back sides of Si layer 102 with thicknesses of approximately 120+20 nm. In an exemplary embodiment, Si layer 102 may be a silicon wafer with a resistance of 0.01 to 0.001 Qm that may include trace amounts of dopants such as antimony or phosphorus in the ppm range. In an exemplary embodiment, Si layer 102 may include other common dopants known in the art or may include no dopants.
[0031] In an exemplary embodiment, preparation of substrate 10 may further include depositing a front silicon nitride layer 106a on first front silicon oxide layer 104a and a back silicon nitride layer 106b on first back silicon oxide layer 104b by a plasma-enhanced chemical vapor deposition (PECVD) method. In an exemplary embodiment, silane (SitF) and ammonia (NH3) gasses may be utilized as reactants in a PECVD method for depositing front silicon nitride layer 106a and back silicon nitride layer 106b. In an exemplary embodiment, after growing first front silicon oxide layer 104a and first back silicon oxide layer 104b on Si layer 102 by thermal oxidation, front silicon nitride layer 106a may be deposited on first front silicon oxide layer 104a, and back silicon nitride layer 106b may be deposited on first back silicon oxide layer 104b with thicknesses of approximately 300+20 nm. In an exemplary embodiment, deposition of front silicon nitride layer 106a and back silicon nitride layer 106b may be performed in a low-pressure chemical vapor deposition (LPCVD) furnace at temperatures of approximately 700 °C to 850 °C.
[0032] In exemplary embodiments, substrate 10 may be either a double-side polished substrate or a single-side polished substrate. A double-side polish may be performed on substrate 10 to flatten front and back sides of substrate 10, or a single-side polish may be performed on substrate 10 to flatten front side of substrate 10.
[0033] FIG. 2A illustrates a flowchart of a method 20 of fabricating an AFM probe, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, method 20 may include a step 22 of forming a handle layer on a backside of a substrate, a step 24 of forming an AFM tip on a front side of the substrate, and a step 26 of forming an AFM cantilever integrated with the AFM tip.
[0034] FIG. 2B illustrates a flowchart for performing step 22 of forming a handle layer on a backside of a substrate, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, the substrate may be a substrate similar to substrate 10, which may include Si layer 102 with first front silicon oxide layer 104a and first back silicon oxide layer 104b grown on Si layer 102 and front silicon nitride layer 106a and back silicon nitride layer 106b deposited on silicon oxide layers (104a and 104b). In an exemplary embodiment, step 22 of forming a handle layer on a backside of a substrate may include a step 220 of transferring a location of a handle window to the backside of the substrate by a photolithographic method and a step 222 of etching a first back silicon oxide layer and a back silicon nitride layer at the location of the handle window. FIG. IB illustrates substrate 10 with a handle window 108 opened on first back silicon oxide layer 104a and back silicon nitride layer 106b thereof, consistent with one or more exemplary embodiments of the present disclosure.
[0035] In an exemplary embodiment, step 220 of transferring a location of a handle window to the backside of the substrate by a photolithographic method may include forming a photoresist mask on the backside of substrate 10 and baking substrate 10 to solidify the photoresist mask for creating a more durable mask for performing later etching steps. For example, substrate 10 may first be washed utilizing acetone and deionized water, and then substrate 10 may be dried with nitrogen. After that, a layer of a photoresist such as Shipley 1813 may be coated onto the substrate 10 utilizing a spin coater. Then, the coated photoresist may be pre-baked at a temperature of approximately 90 °C for approximately 1 minute. A chrome mask with a pattern defining the location of handle window 108 may be placed on the backside of substrate 10 by a hard contact method, and then the backside may be exposed to an intense light with an intensity of approximately 1300 W/cm3 and a wavelength of approximately 405 nm. After that, substrate 10 may be placed inside a standard developer solution for approximately 25 seconds, and then substrate 10 may be rinsed and dried. In the next step, substrate 10 may be baked at 120 °C for approximately 2 minutes.
[0036] In an exemplary embodiment, step 222 of etching a first back silicon oxide layer and a back silicon nitride layer at the location of the handle window may include etching a portion of the backside of the substrate not covered by the photoresist mask. This portion of the backside of the substrate not covered by the photoresist mask was referred to as the handle window in preceding paragraphs. In an exemplary embodiment, back silicon nitride layer 106b may be etched by an etching method such as a reactive ion etching method, where a chemically reactive plasma such as SF6 plasma may be used to remove a portion of back silicon nitride layer 106b not covered by the photoresist mask at the location of handle window 108. For example, a reactive ion etching method may be performed on substrate 10, where a 165 seem SF6 gas flow at 250 W may be utilized for patterning back silicon nitride layer 106b for approximately 380 seconds. After etching back silicon nitride layer 106b at the location of handle window 108, the photoresist layer may be washed with acetone and then substrate 10 may be rinsed and dried.
[0037] In an exemplary embodiment, after etching back silicon nitride layer 106b at the location of handle window 108, buffered HF wet etching may be used to etch first back silicon oxide layer 104b at the location of handle window 108. In an exemplary method, first back silicon oxide layer 104b may be etched by buffered HF solution with a concentration of approximately 10 wt. %. In an exemplary embodiment, buffered HF wet etching may be performed on substrate 10 by placing substrate 10 inside a buffered HF solution that may include HF and a 40 wt. % ammonium fluoride (NH4F) solution with a weight ratio of approximately 3:1 (HF: NH4F) for approximately 30 seconds. Then, substrate 10 may be rinsed and dried.
[0038] In exemplary embodiments, after etching back silicon nitride layer 106b and first back silicon oxide layer 104b, Si layer 102 may be exposed at the location of handle window 108 for later etching steps for forming the handle layer.
[0039] In an exemplary embodiment, step 22 of forming a handle layer on a backside of a substrate may further include a step 224 of etching the handle layer within the Si layer through the handle window. FIG. 1C illustrates substrate 10 with a handle layer 110 etched into Si layer 102 thereof, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, KOH solution may be utilized for etching handle layer 110 into Si layer 102. It should be understood that other etching agents may similarly be used for etching handle layer 110 into Si layer 102. In an exemplary embodiment, the backside of substrate 10 may be exposed to an etching solution including KOH at a temperature of approximately 60 °C to 80 °C.
[0040] For example, a wet etching bath may be prepared that may include KOH and isopropyl alcohol and then substrate 10 may be placed within the wet etching bath such that the backside of substrate 10 may be exposed to the wet etching solution. In an exemplary embodiment, the wet etching solution within the wet etching bath may include KOH with a concentration of about 25 wt.% and isopropyl alcohol with a concentration of about 12.5 wt.%. In exemplary embodiments, adding isopropyl alcohol to the wet etching solution may allow for etching handle layer 110 with smooth edges. In an exemplary embodiment, handle layer 110 may be etched into Si layer 102 by exposing the backside of substrate 10 to the wet etching solution at a temperature of approximately 65 °C for approximately 12 hours under stirring. In an exemplary embodiment, etching handle layer 110 into Si layer 102 may be carried out until a thickness 112 of Si layer not etched above handle window 108 may be approximately 20 pm. In an exemplary embodiment, after etching handle layer 110 into Si layer 102, substrate 10 may be rinsed and dried.
[0041] FIG. 2C illustrates a flowchart for performing step 24 of forming an AFM tip on the front side of a substrate, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, step 24 of forming an AFM tip on a front side of a substrate may include a step 240 of transferring a pattern of the AFM tip to the front side of the substrate by a photolithographic method and a step 242 of etching a first front silicon oxide layer and a front silicon nitride layer utilizing the pattern of the AFM tip.
[0042] In an exemplary embodiment, step 240 of transferring a pattern of the AFM tip to the front side of the substrate by a photolithographic method may include forming a photoresist mask on the front side of substrate 10 and baking substrate 10 to solidify the photoresist mask for creating a more durable mask for performing later etching steps. For example, substrate 10 may first be washed utilizing acetone and deionized water, and then substrate 10 may be dried with nitrogen. After that, a layer of a photoresist such as Shipley 1813 may be coated onto the substrate 10 utilizing a spin coater. Then, the coated photoresist may be pre-baked at a temperature of approximately 90 °C for approximately 1 minute. A chrome mask with a pattern defining the location of the AFM tip may be placed on the front side of substrate 10 by a hard contact method, and then the front side may be exposed to an intense light with an intensity of approximately 1300 W/cm3 and a wavelength of approximately 405 nm. After that, substrate 10 may be placed inside a standard developer solution for approximately 25 seconds, and then substrate 10 may be rinsed and dried. In the next step, substrate 10 may be baked at 120 °C for approximately 2 minutes.
[0043] In an exemplary embodiment, step 242 of etching a first front silicon oxide layer and a front silicon nitride layer utilizing the pattern of the AFM tip may include etching a portion of the front side of the substrate not covered by the photoresist mask. FIG. ID illustrates substrate 10 with its first front silicon oxide layer 104a and front silicon nitride layer 106a etched based on the pattern of AFM tip transferred thereto by a photolithography method, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, front silicon nitride layer 106a may be etched by an etching method such as a reactive ion etching method, where a chemically reactive plasma such as SF6 plasma may be used to remove a portion of front silicon nitride layer 106a not covered by the photoresist mask. For example, a reactive ion etching method may be performed on substrate 10, where a 165 seem SF6 gas flow at 250 W may be utilized for patterning front silicon nitride layer 106a for approximately 380 seconds.
[0044] In an exemplary embodiment, after etching front silicon nitride layer 106a, buffered HF wet etching may be used to etch first front silicon oxide layer 104a. In an exemplary method, first front silicon oxide layer 104a may be etched by buffered HF solution with a concentration of approximately 10 wt. %. In an exemplary embodiment, buffered HF wet etching may be performed on substrate 10 by placing substrate 10 inside a buffered HF solution that may include HF and a 40 wt. % ammonium fluoride (NH4F) solution with a weight ratio of approximately 3:1 (HF: NH4F) for approximately 30 seconds. Then, substrate 10 may be rinsed and dried.
[0045] In exemplary embodiments, after etching front silicon nitride layer 106a and first front silicon oxide layer 104a, Si layer 102 may be exposed except for the location of the AFM tip which is covered by the remaining portions of front silicon nitride layer 106a and first front silicon oxide layer 104a. After that, the photoresist layer may be washed with acetone, and then substrate 10 may be rinsed and dried.
[0046] In an exemplary embodiment, step 24 of forming an AFM tip on a front side of a substrate may further include a step 244 of etching the Si layer from the front side of the substrate to form the AFM tip. FIG. IE illustrates substrate 10 with an AFM tip 114 formed on Si layer 102 thereof, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, KOH solution may be utilized for etching Si layer 102 to form AFM tip 114. It should be understood that other etching agents may similarly be used for etching Si layer 102. In an exemplary embodiment, the front side of substrate 10 may be exposed to an etching solution, including KOH at a temperature of approximately 60 °C to 80 °C. For example, a wet etching bath may be prepared that may include KOH and isopropyl alcohol and then substrate 10 may be placed within the wet etching bath such that the front side of substrate 10 may be exposed to the wet etching solution. In an exemplary embodiment, the wet etching solution within the wet etching bath may include KOH with a concentration of about 25 wt.% and isopropyl alcohol with a concentration of about 12.5 wt.%. In exemplary embodiments, adding isopropyl alcohol to the wet etching solution may allow for etching AFM tip 114 with smooth edges. In an exemplary embodiment, AFM tip 114 may be formed on Si layer 102 by exposing the front side of substrate 10 to the wet etching solution at a temperature of approximately 65 °C for approximately 12 hours under stirring. In an exemplary embodiment, after forming AFM tip 114 on Si layer 102, substrate 10 may be rinsed and dried. [0047] Referring back to FIG. 2A, in an exemplary embodiment, after performing step 22 of forming the handle layer on the backside of the substrate and step 24 of forming the AFM tip on the front side of the substrate, method 20 may proceed to step 26 of forming an AFM cantilever integrated with the AFM tip.
[0048] FIG. 2D illustrates a flowchart for performing step 26 of forming an AFM cantilever on a front side of a substrate, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, step 26 of forming the AFM cantilever on the front side of the substrate may include a step 260 of growing a second front silicon oxide layer on the front side of the substrate, a step 262 of growing a second back silicon oxide layer on the backside of the substrate, a step 264 of transferring a pattern of the AFM cantilever to the front side of the substrate by a photolithographic method, a step 266 of etching the second front oxide layer utilizing the pattern of the AFM cantilever, and a step 268 of etching the Si layer from the front side to form the AFM cantilever.
[0049] In an exemplary embodiment, step 260 of growing a second front silicon oxide layer on the front side of the substrate and step 262 of growing a second back silicon oxide layer on the backside of the substrate may be performed simultaneously by placing the substrate with the handle layer and the AFM tip formed thereon in an oxidation furnace at a temperature between approximately 1050 °C and 1100 °C under an agent flow, such as oxygen flow. For example, substrate 10, as shown in FIG. IE with handle layer 110 and AFM tip 114 formed thereon may be placed in an oxidation furnace under a 25 seem oxygen flow at a temperature of approximately 1050 °C for about 90 minutes to form a second front silicon oxide layer and a second back silicon oxide layer thereon with thicknesses of approximately 200 to 300 nm. [0050] FIG. IF illustrates substrate 10 with a second front silicon oxide layer 116a and a second back silicon oxide layer 116b grown thereon, consistent with one or more exemplary embodiment of the present disclosure. In an exemplary embodiment, second front silicon oxide layer 116a may cover the front side of substrate 10, including a top surface of AFM tip 114. In an exemplary embodiment, second back silicon oxide layer 116b may cover a lower surface of handle layer 110.
[0051] In an exemplary embodiment, after performing step 260 of growing a second front silicon oxide layer on the front side of the substrate and step 262 of growing a second back silicon oxide layer on the backside of the substrate, the method may proceed to step 264 of transferring a pattern of the AFM cantilever to the front side of the substrate by a photolithographic method.
[0052] In an exemplary embodiment, step 264 of transferring the pattern of the AFM cantilever to the front side of the substrate by a photolithographic method may include forming a photoresist mask on the front side of substrate 10 and baking substrate 10 to solidify the photoresist mask for creating a more durable mask for performing later etching steps. For example, substrate 10 may first be washed utilizing acetone and deionized water, and then substrate 10 may be dried with nitrogen. After that, a layer of a photoresist such as Shipley 1813 may be coated onto the substrate 10 utilizing a spin coater. Then, the coated photoresist may be pre-baked at a temperature of approximately 90 °C for approximately 1 minute. A chrome mask with a pattern defining the location of the AFM cantilever may be placed on the front side of substrate 10 by a hard contact method, and then the front side may be exposed to an intense light with an intensity of approximately 1300 W/cm3 and a wavelength of approximately 405 nm. After that, substrate 10 may be placed inside a standard developer solution for approximately 25 seconds, and then substrate 10 may be rinsed and dried. In the next step, substrate 10 may be baked at 120 °C for approximately 2 minutes.
[0053] In an exemplary embodiment, step 266 of etching a second front silicon oxide layer utilizing the pattern of the AFM cantilever may include etching a portion of the front side of the substrate not covered by the photoresist mask. FIG. 1G illustrates substrate 10 with its second front silicon oxide layer 116a etched based on the pattern of AFM cantilever transferred thereto by a photolithography method, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, buffered HF wet etching may be used to etch second front silicon oxide layer 116a. In an exemplary method, second front silicon oxide layer 116a may be etched by buffered HF solution with a concentration of approximately 10 wt. %. In an exemplary embodiment, buffered HF wet etching may be performed on substrate 10 by placing substrate 10 inside a buffered HF solution that may include HF and a 40 wt. % ammonium fluoride (NH4F) solution with a weight ratio of approximately 3:1 (HF: NH4F) for approximately 30 seconds. Then, substrate 10 may be rinsed and dried.
[0054] In an exemplary embodiment, after performing step 266 of etching a second front silicon oxide layer utilizing the pattern of the AFM cantilever, the method may proceed to step 268 of etching the Si layer from the front side to form the AFM cantilever.
[0055] FIG. 1H illustrates substrate 10 with an AFM cantilever 118 formed on Si layer 102 thereof, consistent with one or more exemplary embodiments of the present disclosure. In an exemplary embodiment, KOH solution may be utilized for etching Si layer 102 to form AFM cantilever 118. It should be understood that other etching agents may similarly be used for etching Si layer 102. In an exemplary embodiment, the front side of substrate 10 may be exposed to an etching solution including KOH at a temperature of approximately 60 °C to 80 °C. For example, a wet etching bath may be prepared that may include KOH and isopropyl alcohol and then substrate 10 may be placed within the wet etching bath such that the front side of substrate 10 may be exposed to the wet etching solution. In an exemplary embodiment, the wet etching solution within the wet etching bath may include KOH with a concentration of about 25 wt.% and isopropyl alcohol with a concentration of about 12.5 wt.%. In exemplary embodiments, adding isopropyl alcohol to the wet etching solution may allow for etching AFM cantilever 118 with smooth edges. In an exemplary embodiment, AFM cantilever 118 may be formed on Si layer 102 by exposing the front side of substrate 10 to the wet etching solution at a temperature of approximately 65 °C for a period of approximately 12 hours under stirring. [0056] In an exemplary embodiment, after forming AFM cantilever 118 on Si layer 102, second front silicon oxide layer 116a and second back silicon oxide layer 116b may be etched by buffered HF as was described in the preceding paragraphs. FIG. II illustrates substrate 10 with handle layer 110, AFM cantilever 118, and AFM tip 114 formed thereon, consistent with one or more exemplary embodiments of the present disclosure. Referring to FIG. II, AFM cantilever may be integrally formed with AFM tip 114 as was described. In exemplary embodiments, growing second back silicon oxide layer 116b in step 262 may allow for better control over the thickness of AFM cantilever 118 during step 266, since etching process of Si layer 102 from a front side of substrate 10 may continue down to second back silicon oxide layer 116b. In addition, growing second back silicon oxide layer 116b may allow for maintaining the smoothness of a lower surface (designated by reference numeral 119 in FIG. II) of AFM cantilever 118 while Si layer 102 is being etched by KOH to form AFM cantilever 118 in step 266.
[0057] Exemplary methods of the present disclosure may allow for forming an AFM cantilever with better control over the cantilever thickness while maintaining the smoothness of a back surface of the cantilever during etching steps. Maintaining the smoothness of a back surface of the cantilever by the extra second back silicon oxide layer grown on the substrate after forming the tip and before forming the cantilever may have a considerable effect on reducing the roughness of the back surface of the cantilever and improving the reflective properties of the back surface of the cantilever.
[0058] While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that the teachings may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all applications, modifications and variations that fall within the true scope of the present teachings.
[0100] Unless otherwise stated, all measurements, values, ratings, positions, magnitudes, sizes, and other specifications that are set forth in this specification, including in the claims that follow, are approximate, not exact. They are intended to have a reasonable range that is consistent with the functions to which they relate and with what is customary in the art to which they pertain.
[0059] The scope of protection is limited solely by the claims that now follow. That scope is intended and should be interpreted to be as broad as is consistent with the ordinary meaning of the language that is used in the claims when interpreted in light of this specification and the prosecution history that follows and to encompass all structural and functional equivalents. Notwithstanding, none of the claims are intended to embrace subject matter that fails to satisfy the requirement of Sections 101, 102, or 103 of the Patent Act, nor should they be interpreted in such a way. Any unintended embracement of such subject matter is hereby disclaimed. [0060] Except as stated immediately above, nothing that has been stated or illustrated is intended or should be interpreted to cause a dedication of any component, step, feature, object, benefit, advantage, or equivalent to the public, regardless of whether it is or is not recited in the claims. [0061] It will be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. Relational terms such as first and second and the like may be used solely to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “a” or “an” does not, without further constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.
[0062] The Abstract of the Disclosure is provided to allow the reader to ascertain the nature of the technical disclosure quickly. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various implementations. This is for purposes of streamlining the disclosure and is not to be interpreted as reflecting an intention that the claimed implementations require more features than are expressly recited in each claim. Rather, as the following claims reflect, the inventive subject matter lies in less than all features of a single disclosed implementation. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.
[0063] While various implementations have been described, the description is intended to be exemplary, rather than limiting, and it will be apparent to those of ordinary skill in the art that many more implementations and implementations are possible that are within the scope of the implementations. Although many possible combinations of features are shown in the accompanying figures and discussed in this detailed description, many other combinations of the disclosed features are possible. Any feature of any implementation may be used in combination with or substituted for any other feature or element in any other implementation unless specifically restricted. Therefore, it will be understood that any of the features shown and/or discussed in the present disclosure may be implemented together in any suitable combination. Accordingly, the implementations are not to be restricted except in the light of the attached claims and their equivalents. Also, various modifications and changes may be made within the scope of the attached claims.

Claims

What is claimed is:
1. A method for fabricating an atomic force microscope probe, the method comprising: forming a handle layer on a backside of a substrate, the substrate comprising a silicon layer with a first front silicon oxide layer grown on a front side of the silicon layer and a first back silicon oxide layer grown on the backside of the silicon layer, the substrate further comprising a front silicon nitrate layer deposited on the first front silicon oxide layer and a back silicon nitride layer deposited on the first back silicon oxide layer, forming the handle layer comprising: transferring a location of a handle window to the backside of the substrate by a photolithographic method; etching the first back silicon oxide layer and the back silicon nitrate layer at the location of the handle window; and etching the handle layer within the silicon wafer; forming an AFM tip on the front side of the substrate, forming the AFM tip comprising: transferring a pattern of the AFM tip to the front side of the substrate by a photolithographic method; etching the first front silicon oxide layer and the front silicon nitrate layer utilizing the pattern of the AFM tip; and etching the silicon wafer from the front side to form the AFM tip; and forming an AFM cantilever integrated with the AFM tip by: growing a second front silicon oxide layer on the front side of the substrate, the second front silicon oxide layer covering the front side and the formed AFM tip; growing a second back silicon oxide layer on the substrate, the second back silicon oxide layer covering a surface of the handle layer; transferring a pattern of the AFM cantilever to the front side of the substrate by a photolithographic method; etching the second front silicon oxide layer utilizing the pattern of the AFM cantilever; and etching the silicon wafer from the front side to form the AFM cantilever.
2. A method for fabricating an atomic force microscope probe, the method comprising: forming a handle layer on a backside of a substrate, the substrate comprising a silicon wafer with a first front silicon oxide layer grown on a front side of the silicon wafer and a first back silicon oxide layer grown on the backside of silicon wafer, the substrate further comprising a front silicon nitrate layer deposited on the first front silicon oxide layer and a back silicon nitride layer deposited on the first back silicon oxide layer; forming an AFM tip on the front side of the substrate; and forming an AFM cantilever integrated with the AFM tip by: growing a second front silicon oxide layer on the front side of the substrate, the second front silicon oxide layer covering the front side and the formed AFM tip; growing a second back silicon oxide layer on the substrate, the second back silicon oxide layer covering a lower surface of the handle layer; transferring a pattern of the AFM cantilever to the front side of the substrate by a photolithographic method; etching the second front silicon oxide layer utilizing the pattern of the AFM cantilever; and etching the silicon wafer from the front side to form the AFM cantilever.
3. The method according to claim 2, further comprising etching remainder of the second front silicon oxide layer and the second back silicon oxide layer.
4. The method according to claim 2, wherein growing a second front silicon oxide layer on the substrate and growing a second back silicon oxide layer on the substrate are performed simultaneously by placing the substrate with the handle layer and the AFM tip formed thereon in an oxidation furnace at a temperature between 1050 °C and 1100 °C under oxygen flow.
5. The method according to claim 2, wherein etching the second front silicon oxide layer utilizing the pattern of the AFM cantilever comprises wet etching portions of second front silicon oxide layer not covered by the pattern of the AFM cantilever by a buffered HF solution.
6. The method according to claim 2, wherein etching the second front silicon oxide layer utilizing the pattern of the AFM cantilever comprises wet etching portions of second front silicon oxide layer not covered by the pattern of the AFM cantilever by a buffered HF solution, the buffered HF solution comprising HF and a 40 wt. % ammonium fluoride (NH4F) solution with a weight ratio of 3:1 (HF: NH4F).
7. The method according to claim 2, wherein etching the silicon layer from the front side to form the AFM cantilever comprises etching the silicon layer utilizing a KOH solution at a temperature between 60 °C and 80 °C.
8. The method according to claim 2, wherein forming the AFM tip on the front side of the substrate comprising: transferring a pattern of the AFM tip to the front side of the substrate by a photolithographic method; etching the first front silicon oxide layer and the front silicon nitrate layer utilizing the pattern of the AFM tip; and etching the silicon wafer from the front side to form the AFM tip.
9. The method according to claim 8, wherein etching the first front silicon oxide layer and the front silicon nitrate layer utilizing the pattern of the AFM tip comprises: etching a portion of the front silicon nitrate layer not covered by the pattern of the AFM tip by a reactive plasma etchant; and wet etching portions of the first front silicon oxide layer not covered by the pattern of the AFM tip by a buffered HF solution.
10. The method according to claim 8, wherein etching the silicon layer from the front side to form the AFM tip comprises etching the silicon layer utilizing a KOH solution at a temperature between 60 °C and 80 °C.
11. The method according to claim 2, wherein forming the handle layer comprising: transferring a location of a handle window to the backside of the substrate by a photolithographic method; etching the first back silicon oxide layer and the back silicon nitrate layer at the location of the handle window; and etching the handle layer within the silicon layer.
12. The method according to claim 11, wherein etching the first back silicon oxide layer and the back silicon nitrate layer at the location of the handle comprises: etching the front silicon nitrate layer by a reactive plasma etchant at the location of the handle; and wet etching portions of the first front silicon oxide layer by a buffered HF solution at the location of the handle.
13. The method according to claim 11, wherein etching the handle layer within the silicon layer comprises etching the silicon layer utilizing a KOH solution at a temperature between 60 °C and 80 °C.
PCT/IB2019/058268 2019-09-29 2019-09-29 Fabrication of an atomic force microscope probe WO2021059009A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/IB2019/058268 WO2021059009A1 (en) 2019-09-29 2019-09-29 Fabrication of an atomic force microscope probe

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/IB2019/058268 WO2021059009A1 (en) 2019-09-29 2019-09-29 Fabrication of an atomic force microscope probe

Publications (1)

Publication Number Publication Date
WO2021059009A1 true WO2021059009A1 (en) 2021-04-01

Family

ID=75166498

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB2019/058268 WO2021059009A1 (en) 2019-09-29 2019-09-29 Fabrication of an atomic force microscope probe

Country Status (1)

Country Link
WO (1) WO2021059009A1 (en)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0413042A1 (en) * 1989-08-16 1991-02-20 International Business Machines Corporation Method of producing micromechanical sensors for the AFM/STM profilometry and micromechanical AFM/STM sensor head
US5116462A (en) * 1989-08-16 1992-05-26 International Business Machines Corporation Method of producing micromechanical sensors for the afm/stm profilometry

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0413042A1 (en) * 1989-08-16 1991-02-20 International Business Machines Corporation Method of producing micromechanical sensors for the AFM/STM profilometry and micromechanical AFM/STM sensor head
US5116462A (en) * 1989-08-16 1992-05-26 International Business Machines Corporation Method of producing micromechanical sensors for the afm/stm profilometry

Similar Documents

Publication Publication Date Title
US7210330B2 (en) Methods of fabricating structures for characterizing tip shape of scanning probe microscope probes and structures fabricated thereby
Bhatt et al. Silicon dioxide films by RF sputtering for microelectronic and MEMS applications
US7861316B2 (en) Microscope probe having an ultra-tall tip
US20210080909A1 (en) Process for fabricating a silicon hairspring
Grigoras et al. Application of ultra-thin aluminum oxide etch mask made by atomic layer deposition technique
CN110286432B (en) Preparation method of X-ray gold transmission grating
US20080011066A1 (en) Atomic force microscope cantilever and method for manufacturing the same
WO2021059009A1 (en) Fabrication of an atomic force microscope probe
WO1993014377A1 (en) Method of manufacturing reference samples for calibrating amount of measured displacement and reference sample, and measuring instrument and calibration method
Bongrain et al. Selective nucleation in silicon moulds for diamond MEMS fabrication
KR20070117679A (en) Methods for reducing the curvature in boron-doped silicon micromachined structures
TWI267897B (en) Substrate with anti-reflection layer and its manufacturing method
US20090042372A1 (en) Polysilicon Deposition and Anneal Process Enabling Thick Polysilicon Films for MEMS Applications
US7119332B2 (en) Method of fabricating probe for scanning probe microscope
EP0882944B1 (en) Method of manufacturing a micromechanical sensing probe, in particular for an atomic force microscope
US20060073627A1 (en) Probe for a scanning probe microscope and method for fabricating same
WO2009120343A1 (en) Selective oxidative removal of a self-assembled monolayer for controlled nanofabrication
KR100477365B1 (en) Method for fabricating tip passivation layer in an atomic force microscope
Bodas et al. PMMA As an etch mask for silicon micromachining a feasibility study.
Hanestad et al. Stiction-free release etch with anhydrous HF/water vapor processes
JP3079320B2 (en) Method of manufacturing cantilever for atomic force microscope
Shah et al. Flat single crystal Ge membranes for sensors and opto-electronic integrated circuitry
Hamanaka et al. Fabrication of Self-supported Si Nano-structure with STM
EP1241703B1 (en) Method for masking silicon during anisotropic wet etching
Soave et al. A novel technique for characterizing the surface coverage of thin‐film chemical vapor deposition in ultra‐high‐aspect‐ratio microstructures

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 19946998

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 19946998

Country of ref document: EP

Kind code of ref document: A1