**1. Introduction**

Recently, the interest to design useful nanostructures in science and technology has rapidly increased and these technologies will be superior for the fabrication of nanostructures (Iwanaga & Darling, 2005; Martin et al., 2005; Sadegh Hassani et al., 2010). The patterning of material in this scale is one of the great importances for future lithography in order to attain higher integration density for semiconductor devices (Sadegh Hassani & Sobat, 2011).

Conventional lithography techniques, i.e., those divided to optical and electron beam lithography are either cost-intensive or unsuitable to handle the large variety of organic and biological systems available in nanotechnology. Hence, the various driving forces have been considered for development of nanofabrication techniques (Geissler & Xia, 2004; Quate, 1997; Sadegh Hassani & Sobat, 2011).

Applying of these techniques has started approximately since 1990 and it has given rise to the establishment of different nanolithography methods, which one of the most important method is scanning probe based lithography. An interesting way of performing nanometer pattern is direct scratching of a sample surface mechanically by a probe. The controlled patterning of nanometer scale features with the scanning probe microscope (SPM) is known as scanning probe lithography (SPL) (Irmer et al., 1998). Many reports have been presented about various lithographic methods by this technique (Garcia, 2004; Garcia, 2006). SPL would also be ideal for evaluation of mechanical characteristic of surfaces.

Scanning probe microscopy, such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM), has become a standard technique for obtaining topographical images of surface with atomic resolution (Hyon et al., 1999). In addition, it may be used to study friction force, surface adhesion and modifying a sample surface (Sundararajan & Bhushan, 2000; Burnham et al., 1991; Aime et al., 1994; Sadegh Hassani & Ebrahimpoor Ziaie, 2006; Ebrahimpoor Ziaie et al., 2008). Manipulating surfaces, creating atomic assembly, fabricating chemical patterns and characterizing various mechanical properties of materials in nanometer regime are enabled by this technique (Hyon et al., 1999; Sadegh Hassani & Sobat, 2011; Bouchiat & Esteve, 1996).

Nanolithography with AFM is also a tool to fabricate nanometer-scale structures with at least one lateral dimension between the size of an individual atom and approximately 100 nm on silicon or other surfaces (Wilder & Quate, 1998). This technique is used during the fabrication of leading edge semiconductor integrated circuits (Sugimura & Nakagiri, 1997)

Nanolithography Study Using Scanning Probe Microscope 459

An interesting way of performing nanometer pattern is force lithography which based on direct mechanical impact produced by a sharp probe on the sample surface (Lyuksyutov et al., 2003; Park et al., 2000; Sadegh Hassani et al., 2008a). The probe tip pressure on the surface is sufficient to cause plastic deformation of the substrate surface. This type of modification has been used in nanoelectronics, nanotechnology, material science, etc. It enables the fabrication of electronic components with active areas of nanometer scale, super

In force lithography no bias voltage is required to produce nanostructures. The nanostructure formation normally occurs as a result of AFM tip motion above the polymer surface with set point magnitude constraining the tip to come closer to the surface (Lyuksyutov et al., 2004; Sadegh Hassani et al., 2008a; 2008b; 2010). In order to apply sufficient normal load to reach plastic deformation of surface, a three-side pyramidal single crystalline diamond tip or another tip with high spring constant is used and pressed against a desired surface (Santinacci et al., 2003; Sadegh Hassani et al., 2010). Much higher forces are achieved by accordingly increasing the applied voltage to piezo-scanner. By scanning the sample in the X or Y direction at various conditions (such as different scanning velocity and number of cycles) grooves are created. However, the protrusions along the edges are formed, which indicates clearly stress deformation during the scratching process (Santinacci

It is shown that by applying a little force (severalN), removing an amount of material from

Use of cantilevers with high spring constant could apply the desired amount of force without large bending. When tip move toward the substrate or reverse direction, up or down bending of cantilever occurs, respectively. Since an angle of about 10° is typically set between the cantilever and the substrate (see Fig.1. b), this bending influence the tip– substrate interaction, so the geometry and size of scratches are affected in this way. However, increase of applied force cause cumulating of material along or at the end of the grooves. This deformity is occurred because of cantilever bending at the start point of moving tip through the surface. In this way cantilever reach the desired force to create

Fig. 1. Typical silicon cantilever with pyramidal tip: (a) upper view; (b) lateral view showing the 10° angle formed with the substrate surface; (c) cantilever bending and (d) torsion

dense information recording and study of mechanical properties of material.

a metal or polymer film is possible (Bruckl et al., 1997).

scratch. (Notargiacomo et al., 1999; Sadegh Hassani & Sobat, 2011).

**2. Force lithography** 

et al., 2005).

(Notargiacomo et al., 1999).

or nanoelectromechanical systems (NEMS). This method is not restricted to conductive materials (Fonseca Filho et al., 2004). The advantages of this technique are high resolution and alignment accuracy, which could not be achieved by conventional lithographic techniques (Sheehan & Whitman, 2002; Martin et al., 2005). Moreover, the AFM nanolithography technique takes advantages of the ability to move a probe over the sample in a controllable way (Samori, 2005). Nanolithography using AFM can be done in various modes (Jones et al., 2006): chemical and molecular patterning (DPN), mechanical patterning by scratching or nanoindentation, local heating, voltage bias application and manipulation of nanostructures. Most popular AFM lithographic techniques are resist film lithography (Li et al., 1997) and lithography by oxidation (Sheglov et al., 2005; Sugimura et al., 1993; Sadegh Hassani et al., 2008a; Dubois & Bubbendroff, 1999; Avouris et al., 1998; Snow et al., 1999; Lemeshko et al., 2005; Avouris et al., 1997). The atomic force microscope has also become an increasing popular tool for manipulating thin films of many different types of materials. Lithography techniques can be carried out on the film of polymers such as polymethylmethaacrylate (PMMA), chloromethyl phenyltrichlorosilan (CMPTS), polyethylene (PE) and others (Lee et al., 1997; Sadegh Hassani et al., 2008b, Yoshimura et al., 1993; Chen et al., 1999; Huang et al., 2001). This capability can potentially be extended to evaluate nano-scale material response to indentation and would be ideal for evaluation of mechanical characteristic of surfaces (Burnham & Colton, 1989; Hues et al., 1994; Sadegh Hassani et al., 2008b).

To apply force optimally for making nano scratches, we require to understand the underlying behavior and parameter that control it, a tip which is optimized for applying force under the experimental conditions and scanning techniques which allows one to use these tips and retain desired properties (Yasin et al., 2005; Sadegh Hassani et al., 2008a; 2010). Some factors such as resolution, accuracy of alignment and reproducibility are important in this way. By reducing wear of AFM tip and controlling variables such as applying force, scan speed and environment, it can be systematically calibrated the size of features that is written by AFM tip. So, the reproducibility of issues can be controlled.

In this chapter, it is focused on the use of lithography process to build the desired nanostructures and nanolithography on surface of different substrates by AFM. Creating the scratches on various surfaces by silicon nitride and diamond tips using contact mode is discussed. For scratching, the mechanical action of the tip as a sharp pointed tool in order to produce fine scratches is used (Notargiacomo et al., 1999; Sadegh Hassani et al., 2010). The direct scratching is possible with high precision but low quality results are obtained due to probe wear during lithographic process.

Silicon nitride cantilever tip with average spring constant is used to investigate soft surfaces including poly methyl methacrylate (PMMA) (LG-IH 830) thin film coated on the silicon and glass substrates (Sadegh Hassani et al., 2008a). A diamond cantilever tip with high spring constant is used for hard surfaces including highly-oriented pyrolytic graphite (HOPG) and polyethylene substrate (Sadegh Hassani et al., 2010). Since its hardness is much more than silicon nitride, the direct formation of nanoscratches could easily be achieved.

Effects of applied normal force, time of applying pressure, speed and number of scratching cycles on the geometry and depth of scratches are studied. This study shows that there is a critical tip force to remove material from various surfaces (Sadegh Hassani et al., 2008a; 2008b; 2010).
