Microscopic four-point probe based on SU-8 cantilevers

Giovanni Boero, Jürgen Brugger, Stephan Keller, Schahrazede-Lila Mouaziz
2005
Article

Résumé

A microscopic four-point probe (micro4PP) for resistivity measurements on thin films was designed and fabricated using the negative photoresist SU-8 as base material. The device consists of four microscopic cantilevers, each of them supporting a probe tip at the extremity. The high flexibility of SU-8 ensures a stable electrical point contact between samples and probe tip with all four electrodes even on rough surfaces. With the presented surface micromachining process, micro4PPs with a probe-to-probe spacing of 10–20 um were fabricated. Resistivity measurements on thin Au, Al, and Pt films were performed successfully. The measured sheet resistances differ by less than 5% from those obtained by a commercial macroscopic resistivity meter. Due to the low contact forces (Fcont10^6 ohm/?.

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Microscopic four-point probe based on SU-8 cantilevers

Giovanni Boero, Jürgen Brugger, Stephan Keller, Schahrazede-Lila Mouaziz

A microscopic four-point probe (u4PP) for resistivity measurements on thin films was designed and fabricated using the negative photoresist SU-8 as base material. The device consists of four microscopic cantilevers, each of them supporting a probe tip at the extremity. The high flexibility of SU-8 ensures a stable electrical point contact between samples and probe tip with all four electrodes even on rough surfaces. With the presented surface micromachining process, u4PPs with a probe-to-probe spacing of 10–20 um were fabricated. Resistivity measurements on thin Au, Al, and Pt films were performed successfully. The measured sheet resistances differ by less than 5% from those obtained by a commercial macroscopic resistivity meter. Due to the low contact forces (Fcont10^6 ohm/.

2005

Chargement

The four-point probe is used for the measurement of the resistivity of thin metal or semiconductor films. There is an interest in miniaturization of the probes to obtain higher surface sensitivity, an increased spatial resolution and less damage to the sample. In this project the design, fabrication and first characterisation of a microscopic four-point device using SU-8-cantilevers were realized. A 200-µm-thick SU-8 body chip allows the handling of the device and the electrical connection to the measurement set-up. A SU-8 cantilever with 10 µm thickness is split into four equally spaced micro-cantilevers at its freestanding extremity, each of them supporting a probe tip. This design and the high flexibility of SU-8 ensure a stable electrical point-contact between samples and probe tips. The microscopic four-point probe is fabricated by surface micromachining using silicon as substrate and polysilicon as sacrificial layer. The mould for the probe tips is etched by KOH. 50 nm-Pt, 20 nm-Ti and 300 nm-Al are deposited by sputtering. The metal layer is structured using a chlorine-based plasma dry etch. Two steps of SU-8 photolithography result in the structure of the thin cantilevers and the thick body chip. The entire device is finally released by dry etch of the sacrificial layer with SF6. The smallest probe spacing achieved is 10 µm. The fabricated micro-four-point probes were used to measure the sheet resistance of a 140–nm-thick evaporated gold film. A first series of four-point measurements with a fabricated microscopic SU-8-device having a probe-to-probe spacing of 20 µm resulted in a mean value of sheet resistance Rs(µ4pp)=1.57E-6 Ω/square. This value is comparable to the one of Rs(omnimap)=1.52E-6 Ω/square measured with the commercialised Omnimap RS75 resistivity meter from KLA Tencor.

2005

Chargement

Microscopic four-point probe (u4PP) based on SU-8 cantilevers

Giovanni Boero, Jürgen Brugger, Stephan Keller, Schahrazede-Lila Mouaziz

Four-point probes (4PPs) are used for the resistivity measurement of thin metal or semiconductor films. There is an interest in miniaturization of 4PPs to obtain higher surface sensitivity, increased spatial resolution and less damage to the sample. Several attempts have been made to reduce the probe spacing, e.g. a four-tip scanning tunneling microscope (STM) was reported and a 4PP based on silicon cantilevers was designed. This paper shows design, fabrication and characterisation of a micrometer scale 4PP (micro4PP) device based on SU-8-cantilevers. The photoresist SU-8 has appropriate mechanical properties that make it an excellent candidate material for active parts in selecterd micro-mechanical applications such as cantilevers for scanning probe methods.

2005

Chargement