DE19622701A1

DE19622701A1 - Cantilever chip for atomic force microscopy

Info

Publication number: DE19622701A1
Application number: DE19622701A
Authority: DE
Inventors: Kirsten Ingolf Schiffmann; Xin Dr Jiang; Holger Luethje
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 1996-06-05
Filing date: 1996-06-05
Publication date: 1997-12-18

Abstract

The cantilever chip has a cantilever spring blade provided at its end with a diamond point, which is directly applied to the spring blade via a plasma deposition process. The spring blade may be provided with a diamond layer for modifying its mechanical characteristics. The diamond point and/or the cantilever spring blade may be doped for modifying its electrical characteristics, to allow the simultaneous measurement of the topography and the electrical surface characteristics.

Description

State of the art

Die Rastersondenmikroskopie und darunter speziell die Rasterkraftmikroskopie (Atomic Force Microscopy, AFM) ist ein Verfahren zur Abbildung und Prüfung von Oberflächen mittels einer hochfeinen Abtastspitze, die am Ende einer kleinen bieg samen Blattfeder (Cantilever) befestigt ist (siehe Abb. 1). Diese Spitze kann derart über die Oberfläche einer Probe bewegt werden, daß lokal die Oberflächentopo graphie oder andere Materialeigenschaften wie z. B. Reibwert, Elastizität, Härte, Verschleiß, elektrische Leitfähigkeit, etc. detektiert werden können. Daneben kann die Spitze auch zur mechanischen Strukturierung (Kratzen, Ritzen, Hämmern, etc.) von Oberflächen auf der Mikro- und Nanometerskala eingesetzt werden. Kritischer Faktor hierbei ist die mechanische Festigkeit der Spitze. Bisher verwende te Spitzen aus Silicium oder Siliciumnitrid sind im allg. nicht hart bzw. verschleißfest genug um für Härte,- Verschleiß- oder Strukturierungsarbeiten an harten Oberflä chen eingesetzt werden zu können. - Bisherige Lösungsansätze bestehen in dem Aufkleben einzelner Diamantkristallite auf AFM-Cantilever (siehe z. B.: Bhushan, Ko inkar; Appl. Phys. Lett 64 (1994) 1653, bzw. Persch, Born, Utesch; Appl. Phys A 59 (1994) 29) bzw. im Überziehen konventioneller Spitze einschließlich Cantilevers mit einem dünnen Diamantfilm (Chu et al; Appl. Phys. Lett 63 (1993) 3446 und Germann, McClelland, Mitsuda, Buch, Seki; Rev. Sci. Instr. 63 (1992) 4053). Beides sind jedoch unbefriedigende Lösungen, da im ersten Fall eine Produktion größerer Mengen sol cher Spitzen (wegen Handarbeit) zu aufwendig ist und sich im letzteren Fall eine körnige Spitzengeometrie und schlechtere Diamantqualität (sehr kleiner Diamantkri stallite) nachteilig auswirken können.Scanning probe microscopy, including atomic force microscopy (AFM) in particular, is a procedure for imaging and testing surfaces using a very fine scanning tip that is attached to the end of a small, flexible leaf spring (cantilever) (see Fig. 1). This tip can be moved over the surface of a sample so that locally the surface topography or other material properties such as. B. coefficient of friction, elasticity, hardness, wear, electrical conductivity, etc. can be detected. In addition, the tip can also be used for mechanical structuring (scratching, scratching, hammering, etc.) of surfaces on the micro and nanometer scale. The critical factor here is the mechanical strength of the tip. Tips made of silicon or silicon nitride used up to now are generally not hard or wear-resistant enough to be used for hardness, wear or structuring work on hard surfaces. - Previous approaches have been to glue individual diamond crystallites onto AFM cantilevers (see e.g. Bhushan, Ko inkar; Appl. Phys. Lett 64 (1994) 1653, or Persch, Born, Utesch; Appl. Phys A 59 ( 1994) 29) or in coating conventional tips including cantilevers with a thin diamond film (Chu et al; Appl. Phys. Lett 63 (1993) 3446 and Germann, McClelland, Mitsuda, Buch, Seki; Rev. Sci. Instr. 63 ( 1992) 4053). However, both are unsatisfactory solutions, since in the first case the production of larger quantities of such tips (because of manual work) is too complex and in the latter case a granular tip geometry and poorer diamond quality (very small diamond crystals) can have an adverse effect.

The new process

Es wird deshalb vorgeschlagen einzelne Diamantkristallite von Mikrometerdimen sionen mit Hilfe eines Plasmadepositionsverfahrens (Chemical Vapour Deposition, CVD) direkt auf Siliziumcantilevern aufwachsen zu lassen.Individual diamond crystallites of micrometer dimensions are therefore proposed sions using a plasma deposition process (Chemical Vapor Deposition, CVD) to grow directly on silicon cantilevers.

Dafür können der sog. Hot-Filament-CVD-Prozeß bzw. der sog. Mikrowellen- Plasma-CVD-Prozeß eingesetzt werden, welche sowohl die Herstellung statistisch orientierter wie auch heteroepitaktischer (d. h. parallel zu Kristallstruktur des Substrates orientierter) Diamanten erlauben. Die so erzeugten Spitzen bestehen aus Diamantvollmaterial hoher kristalliner Qualität, haben einige Mikrometer Größe und sind fest mit der Unterlage (Cantilever) verwachsen. Die Geometrie der Abtast spitze läßt sich durch Wahl der Herstellungsparameter so optimieren das Krüm mungsradien von 10 nm bis 1000 nm realisierbar sind. Durch das Herstellungsverfah ren lassen sich eine größere Anzahlen von Spitzen in Form von Chips auf Siliziumwa fern herstellen, wodurch eine wirtschaftliche Produktion derartiger Spitzen ermög licht wird.The so-called hot filament CVD process or the so-called microwave Plasma CVD processes are used, which are both statistical oriented as well as heteroepitaxial (i.e. parallel to the crystal structure of the Allow substrates oriented) diamonds. The peaks thus generated consist of Solid diamond material of high crystalline quality, a few micrometers in size and are firmly attached to the base (cantilever). The geometry of the scan tip can be optimized by choosing the manufacturing parameters Radii of 10 nm to 1000 nm can be achieved. Through the manufacturing process A larger number of tips can be found in the form of chips on silicon wafers remotely, allowing economical production of such tips light becomes.

Claims

1. scanning and test tip consisting of a micro bar (cantilever) with a diamond tip for use in scanning systems and scanning probe microscopes, characterized in that the diamond tip and micro bar form a technological unit such that the diamond tip as a whole using plasma deposition processes directly on the Beam grew up.

2. Probe and test tips according to 1, the cantilever with a diamond layer is covered to modify its mechanical properties.

3. scanning and test tips according to 1, wherein diamond tip and / or cantilever do tated or undoped to modify the electrical properties ren. The electrically conductive diamond probe enables the simul tane scanning force and scanning tunneling microscopy, as well as simultaneous imaging of topography and electrical surface properties.

4. scanning and test tips according to 1, the cantilevers additionally with a piezo resistive layer and be appropriately structured, which makes it possible The bending of the cantilever and thus the movement of the scanning becomes light peak without an external detection system (e.g. laser reflection, interferometry, no capacitive, tunnel current) by tapping an electrical signal from the piezore sistive layer for measuring and for controlling the atomic force microscope Zen.

5. Manufacture of the "diamond tip and cantilever" system using one of the following two methods:

5.1 Additive process: Pre-structuring of a silicon substrate (e.g. by thermal oxidation of all other surfaces) in such a way that diamond grows only at selected points (see Fig. 2). In the following diamond coating process, the nucleation and the growth process of the diamond is controlled in such a way that only individual crystallites grow and selected crystal surfaces have the greatest growth rate. In this way, z. B. generate pyramid-shaped single-crystal diamond tips.
5.2 subtractive process: full-surface coating of a silicon substrate with an oriented diamond film, followed by working out the tips using a lithographic multi-layer process (see Fig. 3). For this purpose, the diamond layer is first z. B. covered metallic layer, on which a photoresist is then applied. The photoresist is structured and the structures are transferred into the metal layer by an etching process. In a second reactive ion etching process, e.g. B. with an oxygen / argon plasma, the structures of the metal layer in the diamond layer are transfe, whereby oblique edges are formed by the directional characteristic of the etching process in the etching mask, which are transferred as the etching process progresses into the diamond layer and finally to form Sharpen.
5.3 For both methods 1.1 and 1.2, the cantilevers are manufactured using the lithographic microstructuring techniques in the following steps (see Fig. 4):
- 5.3.1 The etching of a membrane of silicon a few micrometers thick, whereby the solid mounting parts and thinner bridges between the chips remain. The cantilevers are later formed from the membrane. The thickness of the membrane must therefore correspond to the cantilever thickness.
- 5.3.2 The diamond tips are then integrated on the unetched wafer side using the additive or subtractive method.
- 5.3.3 Finally, the holding part and the cantilever of the chip are covered by lacquers and the remaining silicon membrane is removed by a further etching step, so that the chip is free and is only held at the thin bridges (predetermined breaking points).