This Small Business Innovation Research Phase I project will focus on the development and scale-up of a new process for fabricating probe tips for atomic force microscopy (AFM). In AFM, images of surfaces with atomic-scale resolution are created by rastering a probe across the surface. The probe itself consists of a tip (which interacts with the surface) and a body (which supports the tip and provides an externally-readable signal). The tip radius of curvature determines the size of the smallest surface feature that may be imaged, and the tip composition establishes its hardness and thus its wear resistance. One of the main impediments to wider adoption of AFM has been the poor durability of probe tips. This project will lead to the first batch process to fabricate tips that are both extremely sharp and hard. The new process involves two steps. First, chemical vapor deposition (CVD) is used to coat the tips with a chemically inert and extremely hard material. Second, field directed sputter sharpening (FDSS) sharpens the probe tip to atomic dimensions.
The broader impacts/commercial potential of this project are significant. At present, the CVD/FDSS process has been implemented for coating and sharpening only one tip at a time in a laboratory setting. The current project, which will develop batch wafer-scale processing so that dozens or hundreds of tips can be coated and sharpened at once, will form the basis for a process to manufacture and sell AFM probe tips that are ultra-sharp, very hard, and relatively inexpensive. The availability of such probe tips could lead to a significant expansion of the market for AFM probe tips, which is currently approximately $35 million per year and growing rapidly. The results will significantly enhance the capabilities of all probe microscopy methods, including AFM and related techniques such as scanning spreading resistance microscopy (SSRM) and electrochemical imaging (ECAFM). The research will also be of benefit to those who image insulating surfaces, such as polymers and other soft materials where static charge build-up limits efficacy. In addition, the results of this project could be extended to multi-tip probe arrays for lithographic and nanomanufacturing applications, and to the on-board testing of integrated circuits for delay faults, a capability of great interest to the microelectronics industry.
Intellectual merit. This Phase I SBIR grant funded efforts toward perfecting and scaling up a newly patented process for fabricating ultra sharp and hard probe tips invented at the University of Illinois. The new process involves two steps. First, chemical vapor deposition (CVD) is used to coat the tips with a chemically inert, highly conductive, and extremely hard material. Second, field directed sputter sharpening (FDSS) sharpens the probe tip to atomic dimensions (less than 5 nm radius of curvature at the tip apex). Although the FDSS process has been demonstrated to work on single tips with a limited variety of coatings, the current project showed the feasibility of batch wafer-scale processing, so that dozens or hundreds of tips can be manufactured at once. In order to bring the technique to market, the following research and development tasks were carried out: (a) developed a batch scale fabricator able to apply the FDSS technique to a 4" Silicon wafer, (b) optimized process conditions to reproducibly sharpen arrays of AFM probes fabricated on 4" wafers, (c) tested the ability of the FDSS technique to sharpen a highly useful hard film material, and (d) assessed performance of batch-fabricated probe tips for typical probe microscopy applications. Based on this success, Tiptek submitted a Phase II proposal at the end of July 2012 to fully develop and commercialize this technology. Broader impacts. Scanning probe microscopy (SPM) methods such as atomic force microscopy (AFM) create images of surfaces by rastering a probe across the surface. The probe itself consists of a tip (which interacts with the surface) and a body (which supports the tip and provides an externally-readable signal). The tip radius of curvature (ROC) determines the size of the smallest surface feature that may be imaged, and the tip composition establishes its hardness and thus its wear resistance. Currently, there is no known batch process to fabricate tips that are both extremely sharp (ROC < 5 nm) and hard (> 15 GPa). Probe tips that are ultrasharp, very hard, conductive, and relatively inexpensive will significantly enhance the capabilities of all probe microscopy methods, including AFM and related techniques such as scanning spreading resistance microscopy (SSRM) and electrochemical imaging (ECAFM). The research will also be of benefit to those who image insulating surfaces such as polymers and other soft materials where static charge build-up limits efficacy. In addition, the results of this project could be extended to multi-tip probe arrays for lithographic and nanomanufacturing applications, and to the on-board testing of integrated circuits for delay faults, a capability of great interest to the microelectronics industry.
