**5. Conclusion**

Ion beam lithography is a versatile technique with several variations of the process. Single focused ion beams of Ga ions have been successfully used for exposure of resist layers, but more common are direct milling or beam-induced deposition or etching of the material. Also implantation of the ions to pattern surfaces has been demonstrated as a powerful

The impact of the addition of chlorine on the masking capability of Ga implanted into Si is shown in Fig. 17. While for low SiCl4 concentration the Ga still shows a significant masking effect, we find that the addition of 30% SiCl4 is sufficient to completely suppress the impact

Fig. 17. Impact of the addition of SiCl4 to the masking capability of Ga implanted by FIB into

The addition of chlorine solves the issue of Ga implantation. However, it negatively impacts the available pool of hard mask materials. Now the hard mask material must not only resist etching by a standard fluorine-based RIE process but also to the added chlorine species. As shown above, Ta exhibits excellent properties during the pattern definition process. However, it does not resist our chlorine-containing etch recipe and thus cannot be

In terms of resolution, the direct hard mask patterning process compares very favourably to FIB direct milling. Since the pattern in the thin hard mask layer is transferred into a thicker layer, slopes with low steepness are imaged into slopes with higher steepness. Thus patterning close to the beam diameter becomes possible. Also the influence of the beam tails and mechanical deformation due to milling-induced strain is minimized. We found that lines down to 40 nm half pith are obtainable in a 10 nm thick Ni hard mask

We conclude that the direct patterning of hard mask materials and subsequent pattern transfer by RIE can help to speed up patterning compared to direct FIB milling. We believe that this method is useful for a number of applications including patterning on uneven

Ion beam lithography is a versatile technique with several variations of the process. Single focused ion beams of Ga ions have been successfully used for exposure of resist layers, but more common are direct milling or beam-induced deposition or etching of the material. Also implantation of the ions to pattern surfaces has been demonstrated as a powerful

of the implanted Ga on the final pattern.

Si in a SF6-based RIE process

employed.

layer.

surfaces.

**5. Conclusion** 

structuring approach. With the emergence of helium ion beams, a new tool with new structuring capabilities is on the market and allows new applications. In this work also several structuring approaches have been discussed including (i) FIB milling (ii) FIBinduced gas-assisted processes (iii) 3D patterning by ion implantation and (iv) patterning my milling of hard mask layers. Due to the versatility of these approaches an increasing amount of applications of IBL for optical systems, sensor devices, in the modification and custom-trimming of microelectronic circuitry as well as in the 'classical' fields of photomask repair and defect analysis of cross-sections may be expected. With the neon ion beam systems on the verge of commercial introduction, this is surely going to remain an exciting field of research. With the multi-beam ion systems reaching maturity, interest in IBL from the side of industrial fabrication can also be expected in the future.

#### **6. References**


Focused Ion Beam Lithography 49

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**3** 

*P.R. China* 

**Atom Lithography: Fabricating Arrays of** 

*Department of Physics, University of Science and Technology of China, Hefei* 

Jianwu Zhang, Zhongping Wang and Zengming Zhang

**Silicon Microstructures Using Self-Assembled** 

**Monolayer Resist and Metastable Helium Beam** 

*The Centre of Physical Experiments, University of Science and Technology of China, Hefei* 

Lithography is a top-down technology to produce sub-micrometer feature sizes for the fundamental research and widespread applications. The conventional optical lithography has been developed to not only make the tiny electronic devices to form the basic circuits in today's computer chips, but also fabricate micro/nano electromechanical systems (MEMS/NEMS). However, the conventional photolithographic techniques have now reached their ultimate spatial resolution because of both the light diffraction and the photoresist restrictions [1]. Alternative techniques for traditional photolithography have been proposed and developed to meet the requirements of a high spatial resolution of sub-100 nm as well as the capability to fabricate an arbitrary structure and achieve mass production [1-10]. Research teams around the word have been investigating alternative techniques including extreme ultraviolet lithography, electron and ion beam lithography, Xray lithography and atom lithography. Each technique has its own advantages and disadvantages, and no one yet knows which one will be the method of choice for the next

The arrays of micro- and nanostructures fabricated on silicon substrates have now attracted more attention for its interesting characteristics in applications such as photonics, electronics, optoelectronics and sensing [11-15]. The array properties can be tuned further by varying the geometry, the doping, the periodicity, and the size of the micro- and nanostructures [11,12]. These controllable and elaborate arrays are commonly fabricated by conventional optical lithography, X-ray lithography, electron-beam or ion-beam lithography [1,16-18]. Unfortunately, there are inherent limitations to pattern over large areas at nanoscale using these lithographical techniques due to the light diffraction, the long-range inter-particle interactions and the proximity effects. To overcome these limitations, it's necessary to develop new alternative techniques with a shorter wavelength and a thinner

Among the alternative techniques for traditional photolithography, atom lithography based on metastable atoms beam (MAB) and self-assembled monolayers (SAMs) has shown significant potential in fabricating arrays of micro- and nanostructures, which is a major goal in nanoscience and nanotechnology [10,19-29]. Metastable atom is one of the atom's electron is

**1. Introduction** 

generation lithography (NGL).

resist for traditional optical lithography.

