| AVS 60th International Symposium and Exhibition | |
| Helium Ion Microscopy Focus Topic | Thursday Sessions |
| Session HI-ThA |
| Session: | Imaging and Lithography with Helium Ions |
| Presenter: | I.-Y. Park, KRISS, Republic of Korea |
| Authors: | I.-Y. Park, KRISS, Republic of Korea B. Cho, KRISS, Republic of Korea C. Han, KRISS, Republic of Korea J. Kim, KRISS, Republic of Korea S.J. Ahn, KRISS, Republic of Korea |
| Correspondent: | Click to Email |
The ultra-sharp tips are an essential part for probing and charged particle beam generation in current high resolution microscope. There are a lot of required conditions of tip fabrication and preparation for the high performance of microscopes. Among them, tip cleanliness is very important for the stable and high charged particle current. Here, we describe a simple and efficient method to clean the tungsten tip under UHV(ultra-high vacuum).
Tungsten is preferably adopted for tip material because extremely sharp tip can be easily obtained through electrochemical etching and has higher evaporation field value than ionization field value of rare gases. However, the drawback is poor resistance to surface oxidation; also the surface is contaminated during etching and exposure to atmosphere. In order to eliminate the contaminants, a proper annealing treatment in UHV can remove the contaminant from the tip surface and field evaporation (desorption) can eliminate intensively in the vicinity of the tip apex. In case of annealing, the tip is generally cleaned at approximately 1000 K for several seconds or minutes. However, high temperature could induce the surface diffusion which causes atoms to migrate from the tip apex to tip shank, thereby increasing the radius of tip[1]. Field evaporation cleaning method needs the ultra-sharp tip to produce the field enhancement at the end of tip with a few kV, otherwise it is difficult due to breakdown of high voltage. The nitrogen gas reaction with tungsten surface can sharpen the tip until atomically defined level[2], so we adopted this phenomenon to clean the tip which rarely occur field evaporation with less than 10 kV due to large radius of tip. Firstly, we annealed the tip about 700 K for a few seconds. After that, we inject the nitrogen gas around 10-8 mbar and helium gas up to 10-5 mbar to observe directly the cleaning process through an atomic-scale FIM(field ion microscope) in real time. We can monitor the cleaning and sharpening process simultaneously with FIM. This whole process starts from a base pressure in the low 10-10 mbar range; during the cleaning, the chamber is back filled with 10-5 mbar. On this, vacuum pressure returns to the 10-10 mbar with pumping system. The technique considered here can find applications in blunt tip cleaning and making from blunt tip to the few atom tip sequentially in UHV condition.