Self-Actuated Scanning Probe Tips

The AFM(Atomic Force Microscope) is not only a powerful tool for observing the surface topology with nanometer resolution but also a good candidate for various applications such as high density data storage and nano lithography. Typically, most of previous AFM probe tips have been made of SOI wafers using back-side anisotropic silicon etch. Therefore, the wafer cost is high and the dimension control is poor and the tip length and thickness are affected by variations in wafer thickness and etch rate. Instead of using buried oxide layer in SOI wafers as an etch stop in anisotropic etchant, heavily boron-doped layer can be used as an etch stop layer. With a heavily boron-doped cantilever realized in <100> silicon wafers, there is a silicon barrier at the backside of the cantilever as a result of anisotropic etch characteristics. Back-side alignment is essential in case of <100> and SOI wafers. By using <110> silicon wafers, probe tips are released in anisotropic etchant as the <111> face is located perpendicular to the cantilever.

Below pictures show the AFM probe tip fabricated using <110> silicon wafer with boron-doped cantilever and the enhanced view of the end of cantilever showing the (111) plane of the <110> silicon waver.

The cantilever thickness is the critical factor which determine the mechanical characteristics of the AFM probe tip. The cantilever thickness can be easily controlled by adjusting the boron diffusion time. The sharpness of the end of tip determines the quality of the scanning image. Below pictures show the cantilever thickness according to the diffusion time and the enhanced picture of the tip.

Below picture show the scanning images scanned with the fabricated AFM probe tip. The Left picture is the non-contact mode scanning image and the right picture is the contact mode scanning image.

The AFM probe tips can be actuated using PZT actuator. The left picture shows the AFM probe tip with PZT actuator using heavily-born doped layer. The right picture shows the deflection of the cantilever according to the operation voltage.

Related Publication
  1. Il-Joo Cho, Eun-Chul Park,Euisik Yoon,"AFM Probe Tips Using Heavily Boron-Doped Silicon Cantilevers Realized in a <110> Bulk Silicon Wafer" Digest Papers of Microprocesses and Nanotechnology, pp230-231,2000