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Fabrication method to optimized cantilever anchoring for high performance scanning probe microscopy

IP.com Disclosure Number: IPCOM000076246D
Original Publication Date: 2005-Feb-24
Included in the Prior Art Database: 2005-Feb-24
Document File: 9 page(s) / 790K

Publishing Venue

IBM

Abstract

Fabrication method to optimized cantilever anchoring for high performance scanning probe microscopy

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Fabrication method to optimized cantilever anchoring for high performance scanning probe microscopy

Scanning Probe Microscopies (SPMs) have become an important tool for the characterization of a large variety of surfaces and for the measurement of forces of different physical origin. The cantilevers are recognized as the most critical element in SPMs, intensive efforts have been made to develop various probes to meet the requirements of different SPMs. The cantilever structure consists basically of three parts: - the tip (allowing the very localized interaction with the sample) - the cantilever beam which is basically the spring system - the chip body anchoring the cantilever and allowing the manual manipulation (see 1 and 2 in Fig. 1)

A lot of effort has been put by many different groups to optimize the tip and the cantilever beam which have lead to many different and well established technologies. In contrary, little has been done in optimizing the way the cantilever is anchored, although it is known that it affects the cantilever Q factor, resonant frequency and stiffness. In addition, the present ways to anchor the cantilever are bulky and not precisely controlled, which has some drawbacks like little cantilever chip-sample clearance resulting in difficulties for the cantilever approach and worsening the accessibility of the detection scheme (e.g. laser) to the cantilever. This is clearly an important limitation for cantilever miniaturization. The technologies already developed define the cantilever anchoring point 1 by lithography done on the wafer backside whereas both cantilever and tip are defined from the front side. The tolerance of the wafer thickness and of lithography and bulk micromachining (wet anisotropic etching and deep reactive ion etching) employed to form the support chip results in cantilever anchoring point 1 having much variation from chip to chip in a wafer (in best case 5um) and from wafer to wafer. This variation becomes an issue when scaling down the size of the cantilever by one order of magnitude. Moreover, if the dimension of the anchoring structure is also relatively wide (like in commercial chips > 200 um), it will impose the problem for accessibility of the cantilever to a sample. Therefore the dimension and geometry of the anchoring point should be tailored with cantilever miniaturization.

The motivation in better controlling the anchoring point 1 is to have more freedom in optimizing the cantilever for better performance. As an example, ultra-small, -fast, and -sensitive single-crystal silicon cantilevers (L <30 um, w <5um, and h <250 nm) allow at least 10 times improvement in sensitivity and a factor of 20 enhancement in speed. If the smallness of the cantilevers is not necessarily a challenging aspect of microfabrication, the real issues are the fabrication of the anchoring structure. Another way to improve force sensitivity of SPMs is to optimize the detection scheme. An interferometric schem...