ELSEVIER Sensors and Actuators A 67 ( 1998) 215-219 A PHYSICAL Measurement of micromechanical properties of polysilicon microstructures with an atomic force microscope C. Serre ay*2 P. Gorostiza b3c , A. P6rez-Rodriguez a, F. Sanz b, J.R. Morante a a EME, Dept. Electr&ica, Universitnt de Barcelona, Avda. Diagmal645-647, E-08028 Barcelona, Spain “Dept. Quhica Fisicn, UniLvrsitat de Barcelona, C/Martii Franquh I, E-08028 Barcelona, Spain Senseis CientijcotPcnics, Universitat de Barcelona, C/Sole’ i Sabaris 1-3, E-08028 Barcelotla, Spai?z Abstract A novel, straightforward and convenient method for measurement of micromechanical properties by beam bending using an atomic force microscope in contact mode is presented. This method combines a very high load resolution with a. nanometric precision in the determination of the cantilever deflection, thus allowing accurate measurements to be made. First results applied to the determination of the Young’s modulus of polysilicon cantilever beams are presented. 0 1998 Elsevier Science S.A. All rights reserved. Keywvrds: Mechanical properties; Micromechanical devices; Thin films; Polysilicon; Atomic force microscopes; Young’s modulus 1. Introduction The miniaturization of microelectronic devices is now reaching the mechanical field, allowing the integration of micromechanisms ( sensors, actuators, etc.) together with their operating electronics in a single device. This leads to interesting perspectives in the design of monolithic micro- robotic systems using micromachining techniques directly derived from standard silicon technology [ l-41. This continuous trend requires accurate methods to test and evaluate the mechanical properties of the used films or microstructures. Conventional techniques such as X-ray dif- fraction [ 51 or wafer buckling [ 61 are used for mechanical property measurements on macroscopic specimens. In addi- tion, a Raman microprobe can be used for stress measure- ments at microscopic level [ 7,8]. However, these techniques require a previous knowledge of the elastic parameters of the material. Moreover, a systematic characterization of mechan- ical properties is required for each individual layer, in view of their process dependence. Thus, accurate measurements of these parameters are necessary, and can only be achieved by miniaturizing the test probe to a size approaching the film thickness and the dimensions of the microstructures. Microsized measurements based on the deflection of beams and bridges by nanoindenters have been reported. The deflec- tion can be observed by interferometric methods, or in situ in * Corresponding author. Tel.: +34-3-402-l l-47: Fax: +34-3-302-l I-48: E-mail: serre@irisl.fae.ub.es. 0924-5247/98/$19,00 0 1998 Elsevier Science S.A. All rights reserved. PIISO924-4247(98)00031-4 a scanning electron microscope (SEM) specially modified for this purpose [9-l 1I. This allows the force to be applied with a very good load precision and a thorough position control. However, although resolutions of 0.2-0.4 nm have been achieved in some cases, for example, with the nano- indenter used at Stanford, usually the deflection can only be measured with a resolution of a few hundreds of nanometres. On the other hand, purely tensile pulling procedures were recently developed [ 121 which allowed the measurements of polysilicon Young’s modulus and Poisson’s ratio with a very high precision. However, the method requires a special exten- someter including a piezoelectric stretching mechanism and a laser and fringe detector, and a complex and delicate prep- aration of specially designed specimens. In this work, we describe a novel method for micro- mechanical measurements using an atomic force microscope ( AFM) in contact mode. This method, which does not need any vacuum chamber, combines a very high load resolution with a nanometric precision in the measurement of the can- tilever deflection. Moreover, once the system has been cali- brated, measurements can be performed very quickly and easily. In order to demonstrate the validity of the technique, it has been applied to the determination of the Young’s mod- ulus of micromachined polysilicon beams. 2. Description of the method The method is based on the measurement of the deflection of an end-loaded cantilever beam, where the load is applied