**3.1 Chemically amplified photoresists for applications in microelectronics**

Polymers are probably the most widely used materials for nanopatterning and many different strategies have been developed to achieve a spatial control of the material deposition down to the nanoscale.

As already mentioned previously, Deep-UV (DUV) photolithography has become the current technique used in the industry of microelectronics for production of sub-micron structures. In this field, Chemically Amplified Photoresists (CAR) are the predominant materials used in the fabrication of nanoscale structures with 193 nm photolithography (Bowden & Turner, 1988; Macdonald et al., 1994). Patterns are defined chemically through the production of acid in areas exposed to DUV light (Figure 4) and an acid-catalyzed deprotection reaction that changes the solubility of the reacted material in an aqueous base solution (Ito, 2005). The patterning process is complex since many composition and

for applications in displays, light concentrators for solar cells, displacement sensors or compression of high power laser pulses (Figure 3). The extension of nanostructures over meter square area has generated many efforts. The Fraunhofer Institute fur Solare Energiesysteme (ISE, Freiburg en Brisgau) developed a holographic tool (Holotool) based on a Mach-Zender configuration with an irradiation surface greater than 1 m2. The Lawrence Livermore National Laboratory, in Livermore (Califormia, USA), has developed also an interference lithographic tool compatible with substrates as wide as 80 cm. In both case, the requirements of environmental conditions stability (temperature, mechanical vibrations, etc...) are extremely severe and despite sophisticated monitoring and correctives devices, the

A very interesting alternative has been proposed at Massachusetts Institute of Technology, named Scanning Beam Interference Lithography (SBIL). The principle consists in generating a small area interferometric pattern and then, scans the surface to cover a wide substrate. The main difficulty relies on insuring a controlled displacement at the nanoscale of the writing interferometric head over 1 m2. This is achieved thanks to the development of a sophisticated interferometric displacement sensor. This technique allowed producing 900

Fig. 3. Left) Multilayer dielectric diffraction gratings produced for NIF's Advanced Radiographic Capability petawatt laser have record size, damage resistance and efficieny (www.lasers.llnl.gov) and right) a 300 mm-diameter silicon wafer patterned with a 400 nm-

**3. Polymer-based materials for DUV interferometry lithography** 

**3.1 Chemically amplified photoresists for applications in microelectronics** 

Polymers are probably the most widely used materials for nanopatterning and many different strategies have been developed to achieve a spatial control of the material

As already mentioned previously, Deep-UV (DUV) photolithography has become the current technique used in the industry of microelectronics for production of sub-micron structures. In this field, Chemically Amplified Photoresists (CAR) are the predominant materials used in the fabrication of nanoscale structures with 193 nm photolithography (Bowden & Turner, 1988; Macdonald et al., 1994). Patterns are defined chemically through the production of acid in areas exposed to DUV light (Figure 4) and an acid-catalyzed deprotection reaction that changes the solubility of the reacted material in an aqueous base solution (Ito, 2005). The patterning process is complex since many composition and

resolutions are limited to periods greater than 200 nm.

period grating by the Nanoruler (http://snl.mit.edu/).

deposition down to the nanoscale.

mm x 500 mm gratings.

process parameters have an impact on the photolithographic performances of the photoresist. Among those parameters, those linked to the resist materials are considered as the most critical. Three factors are essential to consider: resolution limit, sensitivity and line-width roughness (LWR). Resolution limit is the most important criterion since the new platforms of resists should be able to address the challenging next lithographic nodes under 45 nm. However, sensitivity is a parameter of importance for practical applications due to the necessity to achieve short exposure times. Line width roughness (LWR) and line edge roughness (LER), measuring the deviation from an atomically smooth surface have also become new parameters preventing the feasibility of smaller feature sizes (Yoshimura et al., 1993).

Fig. 4. a) Molecular mechanism of photoinduced modification of CAR photoresists (positive tone resist). b) SEM images of typical samples prepared by DUV interferometric lithography.

These material requirements for the next generations of DUV lithography have justified the recent efforts to develop innovative photoresists. The cost of industrial lithography tools destined at microelectronics applications (few tens of M\$) is hardly compatible with timeconsuming and potentially contaminant resist development experiments. This is one of the reasons explaining the success of DUV interferometric lithography for developing new photoresists since this tool is relatively easy to install with a reasonable cost, and however, it provides resolutions in the range of the most advanced DUV industrial lithographic tools (few tens of nm). Moreover, immersion lithography or double patterning can be proceeded.

The nature of the polymer significantly contributes to all aspects of resist characteristics and performance. Most of the polymers used as resists are linear copolymers or terpolymers synthesized by the free radical polymerization technique (Ito, 2005; Kang et al., 2006). Such technique has the advantage to be relatively simple but the main drawback is a limited control of the polymer chain structure.

Advanced polymer synthesis strategies like Atom Transfer Radical Polymerization (ATRP) were recently proposed to achieve a better control of the polymer structure, with both linear and hyperbranched structure and for a large variety of monomers (Xia & Matyjaszewski, 2001;

DUV Interferometry for Micro and Nanopatterned Surfaces 251

One of the most important objectives is to propose fast and easy processes to generate hydrophilic/hydrophobic surfaces with nanoscale lateral resolution possibly coupled with topography generation. Such surfaces are of importance for controlled deposition of nano-

In this context, polymers deposited by plasma polymerization have proved to be relevant since they present the following inherent advantages: i) the plasmachemical surface functionalization step is substrate-independent (Boening, 1988), ii) the plasma polymer thin film provides a good adhesion with most of the substrates (Roucoules et al., 2007), iii) the surface density of immobilized molecular species can be finely tuned by varying the pulsed plasma duty cycle (Teare et al., 2002; Oye et al., 2003) and iv) the plasma polymerization

It was recently demonstrated that Deep-UV lithography could be used to generate topography patterns at the surface of maleic anhydride-based plasma polymers with typical dimension down to 75 nm (Soppera et al., 2008). Macroscopic spectroscopic characterization demonstrated that the surface chemistry was affected by DUV-irradiation (Figure 6). The choice of maleic anhydride-based polymer was guided by the reactivity of anhydride moieties that allows the introduction of further functionalities and/or immobilization of bioactive molecules using different binding strategies. These options are very valuable for the preparation of model substrates for fundamental studies on biointerfacial phenomena as well as for the controlled surface modification of a great

> water contact angle e=66°

Fig. 6. Plasma polymer thin film preparation and surface chemistry characterization

<sup>O</sup> <sup>O</sup> <sup>O</sup> <sup>N</sup> <sup>O</sup> <sup>O</sup> <sup>O</sup> <sup>N</sup> <sup>O</sup> <sup>O</sup> <sup>O</sup> <sup>N</sup> HOOC COOH

DUV Irradiation

Propylamine HOOC COOH

substrate

water contact angle e=20°

**35 nm**

**0 nm**

**1.0 µm**

step is easily scaled up to industrial dimension (Yasuda & Matsuzawa, 2005).

substrate substrate

120 °C

objects, for applications in biology, or sensors.

variety of bulk substrates.

<sup>O</sup> <sup>O</sup> <sup>O</sup> <sup>O</sup> <sup>O</sup> <sup>O</sup> <sup>O</sup> <sup>O</sup> <sup>O</sup>

(Soppera et al., 2008; Dirani et al., 2010)

Chochos et al., 2009). Interestingly, a correlation can be obtained between the polymer molecular weight, the chemical composition of the polymer and its polydispersity and its performance in photolithography, for linear and branched polymers, demonstrating the interest of a precise of the polymer molecular structure for nanolithography. (Ridaoui et al., 2010).

#### **3.2 Molecular glass photoresists**

Amorphous molecular glasses were recently proposed as a promising class of photoresists matrixes in addition to the traditional polymeric materials. They are amorphous materials with low molecular weight and designed for DUV, Extreme-UV (EUV) or e-beam lithography (Tsuchiya et al., 2005). Low molecular weight materials can form a stable glass above room temperature and they offer several advantages over traditional linear polymers as patterning feature size decreases. Compared to polymeric resists, molecular glasses provide better control of molecular structure and a broader range of building blocks. The recourse to molecular elementary building blocks allows reducing the variations in line width roughness (LWR) and line edge roughness (LER). In addition, the small uniform molecular size offers excellent processability, flexibility, transparency and uniform dissolution properties based on elemental composition.

Many different molecular structures have been proposed recently. Among other works, Figure 5 illustrates 2 examples. First example is based on an Adamantane architecture (Tanaka & Ober, 2006). Adamantane structure brings both high transparency at 193 nm wavelength and high etch resistance by the cage structure. The second example is a 3 component system composed of a monomer, a crosslinker and a photoacid generator.

Upon irradiation, photoacid is generated in the exposed region. Cross-linking reactions between the TMMGU cross-linker and the hydroxy groups on the monomer are catalyzed by the acid generated during the post-exposure baking period. The resulting cross-linked oligomers are insoluble in aqueous base, thus providing the solubility switch required for development. This system is capable of producing 60 nm line/space patterns (Yang et al., 2006).

Fig. 5. a) Adamantane based molecular glass photoresist (from Tanaka & Ober, 2006) and b) Components of negative-tone molecular glass resist: monomer (1), TMMGU cross-linker (2), and photoacid generator (3) (Yang et al., 2006).

#### **3.3 Plasma polymer for micro and nanopatterned surfaces**

The examples given in the previous parts are in relation with applications in microelectronics that are obviously the most important applications. Besides the fabrication of nanostructures by lithography, the generation of functional materials with chemical control at the nanoscale has drawn considerable interest during the last years.

Chochos et al., 2009). Interestingly, a correlation can be obtained between the polymer molecular weight, the chemical composition of the polymer and its polydispersity and its performance in photolithography, for linear and branched polymers, demonstrating the interest of a precise of the polymer molecular structure for nanolithography. (Ridaoui et al., 2010).

Amorphous molecular glasses were recently proposed as a promising class of photoresists matrixes in addition to the traditional polymeric materials. They are amorphous materials with low molecular weight and designed for DUV, Extreme-UV (EUV) or e-beam lithography (Tsuchiya et al., 2005). Low molecular weight materials can form a stable glass above room temperature and they offer several advantages over traditional linear polymers as patterning feature size decreases. Compared to polymeric resists, molecular glasses provide better control of molecular structure and a broader range of building blocks. The recourse to molecular elementary building blocks allows reducing the variations in line width roughness (LWR) and line edge roughness (LER). In addition, the small uniform molecular size offers excellent processability, flexibility, transparency and uniform

Many different molecular structures have been proposed recently. Among other works, Figure 5 illustrates 2 examples. First example is based on an Adamantane architecture (Tanaka & Ober, 2006). Adamantane structure brings both high transparency at 193 nm wavelength and high etch resistance by the cage structure. The second example is a 3 component system composed of a monomer, a crosslinker and a photoacid generator. Upon irradiation, photoacid is generated in the exposed region. Cross-linking reactions between the TMMGU cross-linker and the hydroxy groups on the monomer are catalyzed by the acid generated during the post-exposure baking period. The resulting cross-linked oligomers are insoluble in aqueous base, thus providing the solubility switch required for development. This

Fig. 5. a) Adamantane based molecular glass photoresist (from Tanaka & Ober, 2006) and b) Components of negative-tone molecular glass resist: monomer (1), TMMGU cross-linker (2),

The examples given in the previous parts are in relation with applications in microelectronics that are obviously the most important applications. Besides the fabrication of nanostructures by lithography, the generation of functional materials with chemical

control at the nanoscale has drawn considerable interest during the last years.

system is capable of producing 60 nm line/space patterns (Yang et al., 2006).

**3.2 Molecular glass photoresists** 

dissolution properties based on elemental composition.

and photoacid generator (3) (Yang et al., 2006).

**3.3 Plasma polymer for micro and nanopatterned surfaces** 

One of the most important objectives is to propose fast and easy processes to generate hydrophilic/hydrophobic surfaces with nanoscale lateral resolution possibly coupled with topography generation. Such surfaces are of importance for controlled deposition of nanoobjects, for applications in biology, or sensors.

In this context, polymers deposited by plasma polymerization have proved to be relevant since they present the following inherent advantages: i) the plasmachemical surface functionalization step is substrate-independent (Boening, 1988), ii) the plasma polymer thin film provides a good adhesion with most of the substrates (Roucoules et al., 2007), iii) the surface density of immobilized molecular species can be finely tuned by varying the pulsed plasma duty cycle (Teare et al., 2002; Oye et al., 2003) and iv) the plasma polymerization step is easily scaled up to industrial dimension (Yasuda & Matsuzawa, 2005).

It was recently demonstrated that Deep-UV lithography could be used to generate topography patterns at the surface of maleic anhydride-based plasma polymers with typical dimension down to 75 nm (Soppera et al., 2008). Macroscopic spectroscopic characterization demonstrated that the surface chemistry was affected by DUV-irradiation (Figure 6). The choice of maleic anhydride-based polymer was guided by the reactivity of anhydride moieties that allows the introduction of further functionalities and/or immobilization of bioactive molecules using different binding strategies. These options are very valuable for the preparation of model substrates for fundamental studies on biointerfacial phenomena as well as for the controlled surface modification of a great variety of bulk substrates.

Fig. 6. Plasma polymer thin film preparation and surface chemistry characterization (Soppera et al., 2008; Dirani et al., 2010)

DUV Interferometry for Micro and Nanopatterned Surfaces 253

opposite behavior of bacteria compared to eukaryotic cells, in response to the surface chemistry and to the surface topography. This result may be particularly useful on medical

Despite many advantages listed below, organic-based polymers have specific limitations like poor mechanical properties, low refractive index and thus, there is a major interest to develop non-organic materials suitable for nanofabrication. In this context, metal oxides present many advantages. As an example, Zirconium dioxide (ZrO2) has unique properties such as high refractive index, wide optical band gap, low absorption and dispersion in the visible and near-infrared spectral regions, as well as high chemical and thermal stabilities. Other metal oxides like TiO2, HfO2, ZnO have many applications in fields like photocatalysis, photovoltaic, displays, biology, optics, and photonics... (Lebeau & Innocenzi,

The chemical sol–gel process is probably the most attractive route to elaborate inorganic thin films due to its powerful control on the structural and properties of films, low-cost, and abilities to deal with substrates of large area and/or complex shape (Judenstein & Sanchez, 1996). It is a versatile process that can be adapted for a wide range of oxides (Si, Zr, Ti, Hf, Zn) using simple deposition techniques (dip-coating, spin-coating) and relatively low curing temperatures (few hundreds of °C). Basically, sol-gel chemistry is based on the succession of

M(OR)4 + H2O —> HO-M(OR)3 + R-OH (2)

M(OR)4 + 4 H2O —> M(OH)4 + 4 R-OH (3)

(OR)3–M-OH + HO–M-(OR)3 —> [(OR)3M–O–M(OR)3] + H-O-H (4)

(OR)3–M-OR + HO–M-(OR)3 —> [(OR)3M–O–M(OR)3] + R-OH (5)

Usually the crosslinking of the layer is achieved by thermal process. In this case, the process is not compatible with photopatterning at the micro or the nanoscale. Several strategies have been developed to achieve patterning on sol-gel deposited thin metal oxide layers. Some examples for ZrO2 are given in (Thomas, 1994; Belleville et al., 2000; Belleville et al., 2003; Zhang et al., 2000; Tian et al. 2005). Usually they rely on complex multistep processes, such as photolithographic patterning and chemical etching or lift-off. These methods often use sacrificial masking materials and the transfer step induces a loss

There is thus a major challenge to develop direct means for nanopatterning. One way consists in proposing hybrid materials based on precursors combining an inorganic function and a photopolymerizable one (Soppera et al., 2003; Matejka et al., 2004). The main limitation of this route is to finally provide a hybrid material with a relatively high

**4. Inorganic materials for DUV interferometry lithography** 

2010) and require convenient techniques for nanopatterning.

hydrolysis and condensation reactions as follow:

Where M stands for different elements (Si, Zr, Ti...)

implants design.

**4.1 Introduction** 

Hydrolysis

Condensation

of resolution.

proportion of organic part.

It was also demonstrated that the DUV patterning allows creating topographic nanopatterns associated to a precise tuning of the local surface chemistry (Dirani et al, 2010a; Dirani et al., 2010b; Soppera et al., 2008). The control of the surface chemistry contrast was achieved by a new method using Atomic Force Microscopy in Pulsed Force Mode with plasma polymer functionalized tips (Figure 7).

Fig. 7. PFM images of the imide plasma polymer surface for increasing DUV dose. The period of pattern was 150 nm. An imide terminated tip was used for surface probing in air. First raw is the topography image. Last raw shows the local pull-off force. Doses of a) 0.75 mJ/cm², b) 1.50 mJ/cm² and c) 3.75 mJ/cm² were used (Dirani et al., 2010)

Fig. 8. Comparison of human osteoprogenitor cells development on non-patterned (left) and patterned (right) plasma polymer surface (Ploux et al., 2009).

These chemically and topographically patterned surfaces have high potential as model surfaces for studying cell and bacteria responses to surface chemistry and surface topography. Biological experiments were conducted on patterned maleic anhydride plasma polymer thin films using human osteoprogenitor cells and Escherichia coli K12 (Ploux et al., 2009). Proliferation and orientation of cells and bacteria were analyzed and discussed according to the size and the chemistry of the features. This work showed interesting opposite behavior of bacteria compared to eukaryotic cells, in response to the surface chemistry and to the surface topography. This result may be particularly useful on medical implants design.

### **4. Inorganic materials for DUV interferometry lithography**

#### **4.1 Introduction**

252 Recent Advances in Nanofabrication Techniques and Applications

It was also demonstrated that the DUV patterning allows creating topographic nanopatterns associated to a precise tuning of the local surface chemistry (Dirani et al, 2010a; Dirani et al., 2010b; Soppera et al., 2008). The control of the surface chemistry contrast was achieved by a new method using Atomic Force Microscopy in Pulsed Force Mode with plasma polymer

Z scale : 0.5 nm Z scale : 1.5 nm Z scale : 3.5 nm

pull-off = 8 nN pull-off = 25 nN pull-off = 53 nN

a) 0.75 mJ/cm² b) 1.50 mJ/cm² c) 3.75 mJ/cm²

functionalized tips (Figure 7).

patterned (right) plasma polymer surface (Ploux et al., 2009).

Fig. 7. PFM images of the imide plasma polymer surface for increasing DUV dose. The period of pattern was 150 nm. An imide terminated tip was used for surface probing in air. First raw is the topography image. Last raw shows the local pull-off force. Doses of a) 0.75

Fig. 8. Comparison of human osteoprogenitor cells development on non-patterned (left) and

These chemically and topographically patterned surfaces have high potential as model surfaces for studying cell and bacteria responses to surface chemistry and surface topography. Biological experiments were conducted on patterned maleic anhydride plasma polymer thin films using human osteoprogenitor cells and Escherichia coli K12 (Ploux et al., 2009). Proliferation and orientation of cells and bacteria were analyzed and discussed according to the size and the chemistry of the features. This work showed interesting

mJ/cm², b) 1.50 mJ/cm² and c) 3.75 mJ/cm² were used (Dirani et al., 2010)

Despite many advantages listed below, organic-based polymers have specific limitations like poor mechanical properties, low refractive index and thus, there is a major interest to develop non-organic materials suitable for nanofabrication. In this context, metal oxides present many advantages. As an example, Zirconium dioxide (ZrO2) has unique properties such as high refractive index, wide optical band gap, low absorption and dispersion in the visible and near-infrared spectral regions, as well as high chemical and thermal stabilities. Other metal oxides like TiO2, HfO2, ZnO have many applications in fields like photocatalysis, photovoltaic, displays, biology, optics, and photonics... (Lebeau & Innocenzi, 2010) and require convenient techniques for nanopatterning.

The chemical sol–gel process is probably the most attractive route to elaborate inorganic thin films due to its powerful control on the structural and properties of films, low-cost, and abilities to deal with substrates of large area and/or complex shape (Judenstein & Sanchez, 1996). It is a versatile process that can be adapted for a wide range of oxides (Si, Zr, Ti, Hf, Zn) using simple deposition techniques (dip-coating, spin-coating) and relatively low curing temperatures (few hundreds of °C). Basically, sol-gel chemistry is based on the succession of hydrolysis and condensation reactions as follow:

Hydrolysis

$$\text{M(OR)}\_{4} + \text{H}\_{2}\text{O} \quad \text{--} \quad \text{HO-M(OR)}\_{3} + \text{R-OH} \tag{2}$$

$$\text{M(OR)4} + 4\text{ H}\_2\text{O} \quad \rightarrow \text{ M(OH)4} + 4\text{ R-OH} \tag{3}$$

Condensation

$$\text{(OR)}\text{-M-OH} + \text{HO-M-(OR)}\_3 \quad \text{---} \quad \text{[(OR)}\text{-M-M(OR)}\_3\text{]} + \text{H-O-H} \tag{4}$$

$$\text{(OR)}\_{3}\text{-M-OR} + \text{HO-M-(OR)}\_{3} \quad \text{---} \quad \text{[(OR)}\_{3}\text{M-O-M(OR)}\_{3}\text{]} + \text{R-OH} \tag{5}$$

Where M stands for different elements (Si, Zr, Ti...)

Usually the crosslinking of the layer is achieved by thermal process. In this case, the process is not compatible with photopatterning at the micro or the nanoscale. Several strategies have been developed to achieve patterning on sol-gel deposited thin metal oxide layers. Some examples for ZrO2 are given in (Thomas, 1994; Belleville et al., 2000; Belleville et al., 2003; Zhang et al., 2000; Tian et al. 2005). Usually they rely on complex multistep processes, such as photolithographic patterning and chemical etching or lift-off. These methods often use sacrificial masking materials and the transfer step induces a loss of resolution.

There is thus a major challenge to develop direct means for nanopatterning. One way consists in proposing hybrid materials based on precursors combining an inorganic function and a photopolymerizable one (Soppera et al., 2003; Matejka et al., 2004). The main limitation of this route is to finally provide a hybrid material with a relatively high proportion of organic part.

DUV Interferometry for Micro and Nanopatterned Surfaces 255

Z (nm)

Fig. 10. AFM image of a periodic patterns written on the Zr sol-gel film. Period was 500 nm. Left) represent the grating before thermal heating, and Right) is a grating after thermal

The development of large-area, high-resolution nanostructures is a challenging problem that must be addressed for applications in high performance nanoscale devices, such as nanoelectronics, optics, microfluidics, organic solar cell, display devices and biosensing devices. Today's challenges are not limited to the resolution issue but many others aspects are to be considered. In particular, there is a growing need for simple processes enabling

With this regards, DUV interferometric lithography techniques are still of high interest, as illustrated in this chapter. The recourse to advanced optical setup and immersion allow creating patterns with typical dimensions much smaller than 100 nm on the basis of many different materials. This photon-based technique is thus competitive in terms of resolution with other advanced nanofabrication techniques and because it is a massively parallel technology to produce nanoparts on a large substrate, it is well-complementary to e-beam,

Agence Nationale pour la Recherche (ANR - Projects NANORUGO, HOLOSENSE and NIR-OPTICS), CNRS and Région Alsace are gratefully acknowledged for financial supports

Archambault, J.-L.; Reekie L. & Russell, P.St.J. (1993). 100% reflectivity Bragg reflectors

produced in optical fibres by single excimer laser pulses. *Electron. Lett*., Vol.29,

0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2 X (nm)

X (µm)

heating (600°C, 2 hours).

integration of functional materials.

No.5, (March 1993), pp. 453-455

ion-beam or nanoimprint.

**6. Acknowledgment** 

**7. References** 

**5. Conclusion** 

**Z (nm)**

0 0,5 1 1,5 2 **X (nm)**

**X (µm)**

#### **4.2 Nanopatterning of hybrid precursors by DUV interferometry**

In order to obtain inorganic nanostructures, sol-gel-based spin-coatable precursor of ZrO2 that is not only amenable to direct-write using DUV lithography but is also capable of providing nanoscale resolution was proposed. (Ridaoui et al., 2010)

The crosslinking photoreaction relies on a direct photolysis of the complexed Zr atom. The interaction between UV light and metal alkoxide complex has been already described : after light absorption, charge transfer complexes can be created and they can induce a photolysis of the ligand (Versace et al., 2008). For Titanium alkoxides, it has been proved that Ti-oxo complex gave rise to a decarboxylation reaction (Hundiecker reaction (Soppera et al., 2001)). In the present case, we can assume that the same kind of mechanism occurs, leading to the production of reactive Zr species that can react on free alkoxides functions to create a tridimensional ZrO2 network (Figure 9).

Fig. 9. Schematic representation of the material preparation and modification under DUV irradiation of the negative tone inorganic resist. M is a transition metal (Zr, Ti…). As shown in this scheme, the DUV irradiation results in condensation of the partially condensed metal alkoxide precursors resulting in a modification of solubility of the thin film (Ridaoui et al., 2010)

The main interest of this negative tone resist relies on the possibility to remove the organic part and obtain ZrO2 after thermal treatment. The AFM scan of the sample is plotted in Figure 10. It can be observed that the patterns remained perfectly defined after the thermal treatment, opening a very convenient way to produce micro or nanostructures. Applications of such nanostructures with high refractive index are expected in the field of optics and photonics. Many applications of such technology are also expected in all applications fields in which robust nanostructures with inertness towards chemical, temperature, and pressure are needed such as photovoltaic, photocatalysis or biology.

Fig. 10. AFM image of a periodic patterns written on the Zr sol-gel film. Period was 500 nm. Left) represent the grating before thermal heating, and Right) is a grating after thermal heating (600°C, 2 hours).
