**3. Ion beam equipment**

For structuring with an ion beam, two complementary approaches have to be distinguished. The equipment setup differs among those approaches described in Table 1. Yet, the experimental setup always includes an ion source and an ion optical system consisting of electrostatic lenses and electrostatic deflectors. For ion optics, only ions of a specific mass and of a specific energy can be used for the focusing optics. From the use of ions for structuring 'resist-based' and 'resistless' methods can be distinguished.


Table 1. Structuring approaches using an ion beam

### **3.1 Ion sources**

The core component of an ion beam system is the ion source. Development of ion sources initially was motivated by mass spectrometry and ion implantation for semiconductor manufacturing. Only with the emerging resolution limits of optical lithography particle beam methods became interesting for nanostructuring. For using a focused beam, a point source is required, while broad beams can also use ion sources emitting ions over a larger area. Four basic ion source types are described below:


Focused Ion Beam Lithography 33

This Taylor cone of liquid metal results in a very high electric field at the cone apex, which is

Fig. 2. Shape of the emitter tip coated with a liquid AuGe alloy (a) without Taylor cone; (b)

observation of the tip shape of AuGe liquid alloy ion sources using a high volt transmission electron microscope. JVST B 14(5), 3367. Copyright 1969, American Vacuum Society..

The ion beam is used for imaging (Orloff et al., 1996), local implantation (Schmidt et al., 1997), physical milling (Giannuzzi & Stevie, 1999), gas-assisted etching (Utke et al., 2008), localized deposition (Matsui et al., 2000) and for exposure of resist layers (J. Melngailis, 1993) (Lee & Chung, 1998) as extensively described in literature (Tseng, 2005); (Giannuzzi & Stevie, 1999)

'Heavy' ions, such as Ga+, may displace and scatter atoms in the substrate so much that device performance suffers. The He ion beam offers a new alternative. Helium ions are more massive than electrons by over three orders of magnitude and thus diffract less around apertures. Thus, smaller apertures are possible in a helium ion column than in an electron column, and this enables a smaller spot size. The specied spot size for a Zeiss Orion Plus helium ion microscope is 0.75 nm at an accelerating voltage of 30 kV. The first commercial helium ion microscope was introduced in 2006 (B. W. Ward et al., 2006) and by now has reached a maturity so that edge resolutions of <0.35 nm have become routinely possible. As ion source a cryogenically cooled metal needle with a tip in the shape of a three-sided pyramid is used. The He+ source can be cooled to around 80 K, which resembles a point source that can be focused. When gun temperature exceeds 95 K, this structure is unstable, meaning source size and thus brightness may become compromised at higher temperatures A small quantity of helium is admitted in the vicinity of the sharp tip in the shape of a threesided pyramid. The apex of the pyramid consists of a set of three atoms, the trimer. The injected helium is then polarized by the large electric field and He atoms accelerate towards ionization area near the three topmost atoms. Only in this restricted area at the pyramidal tip does ionization take place. The charged He ions from one emitter atom are selected and are accelerated into the ion column to produce the focused electron beam. The ion optics

Reprinted with permission from Driesel W., Dietzsch C. & Muhle R., 1969. In situ

(Jeon et al., 2010) (Tseng, 2004) and is therefore not further discussed here in detail.

should theoretically operate around unity magnication.

required for field emission of the ions.

with Taylor cone.

**3.3 He ion microscope** 

Due to the point-like emission of ions from a single spot, the focusing to a beam with an ultra-small diameter is feasible. The adsorbtion of gas on the tip may be enhanced by cryostatic cooling of the tip. The focused ion beam may be used for a field ion microscope and typically non-reactive ions, such as noble gas, ions are used.

4. **Liquid metal ion source (LMIS).** The LMIS operates by desorbtion of metal ions from liquid metal under a strong electrical field. Typically a thin needle or a capillary is wetted by a thin film of liquid source metal, which has been heated to the liquid state. Typically, gallium (m.p. 29,8°C) or indium (m.p. 156,6°C) or Be-Si-Au alloys (Au70Si15Be15) are employed. A Taylor cone is formed under the application of a strong electric field. The force acting onto the needle due to the electric filed shapes the cone's tip to get sharper, until ions are produced by field evaporation. For emission of ions, a threshold extractor voltage (for Ga 2kV) is required. For an alloy source, an energy separator is needed to filter out one ion species. Liquid metal ion sources are particularly used in focused ion beam microscopes. The emission angle is around 30°. The angle distribution of emission current is rather uniform. Energy spread of emitted ions can be large (>15V) resulting in a large chromatic aberration.

Depending on whether a resist layer is used or resistless structuring is performed, patterning with an ion beam opens up different structuring capabilities, as shown in Table 2.


Table 2. Resist-based and resistless patterning approaches with an ion beam

Depending on the selected source type focused beam systems and broad beam systems also have to be distinguished as depicted in Table 3.


Table 3. System configurations with ion beam tools

#### **3.2 Ga ion microscopes**

Focused ion beam tools using a liquid metal ion source for Ga ions are currently the state of the art, because this ion beam can be made very small and therefore resembles a perfect tool for nanofabrication. The Ga ion beam can be focused below 5nm diameter, as the ion source is almost an ideal point source. The original W wire is not sharp and may have a tip radius of more than 1 µm. The sharp tip is formed by the liquid metal induced by the electric field.

microscope and typically non-reactive ions, such as noble gas, ions are used. 4. **Liquid metal ion source (LMIS).** The LMIS operates by desorbtion of metal ions from liquid metal under a strong electrical field. Typically a thin needle or a capillary is wetted by a thin film of liquid source metal, which has been heated to the liquid state. Typically, gallium (m.p. 29,8°C) or indium (m.p. 156,6°C) or Be-Si-Au alloys (Au70Si15Be15) are employed. A Taylor cone is formed under the application of a strong electric field. The force acting onto the needle due to the electric filed shapes the cone's tip to get sharper, until ions are produced by field evaporation. For emission of ions, a threshold extractor voltage (for Ga 2kV) is required. For an alloy source, an energy separator is needed to filter out one ion species. Liquid metal ion sources are particularly used in focused ion beam microscopes. The emission angle is around 30°. The angle distribution of emission current is rather uniform. Energy spread of emitted

ions can be large (>15V) resulting in a large chromatic aberration.

Scanning beam maskless Projection

write Deposition or Direct-write Etching

Table 2. Resist-based and resistless patterning approaches with an ion beam

**Resistless** Direct-write Milling or Direct-

have to be distinguished as depicted in Table 3.

Single beam Sequential writing

Multi-beam Parallel writing

**3.2 Ga ion microscopes** 

slow

fast

Table 3. System configurations with ion beam tools

**Resist** Direct-write exposure of resist Projection exposure

Depending on the selected source type focused beam systems and broad beam systems also

Focused ion beam tools using a liquid metal ion source for Ga ions are currently the state of the art, because this ion beam can be made very small and therefore resembles a perfect tool for nanofabrication. The Ga ion beam can be focused below 5nm diameter, as the ion source is almost an ideal point source. The original W wire is not sharp and may have a tip radius of more than 1 µm. The sharp tip is formed by the liquid metal induced by the electric field.

Depending on whether a resist layer is used or resistless structuring is performed, patterning with an ion beam opens up different structuring capabilities, as shown in Table 2.

**Single focused beam Broad beam** 

Ga LMIS

Plasma source with aperture plate and projection optics

requires mask

Projection milling

**Focused beam Broad beam**  High resolution Low resolution


He-LIS Plasma source

Due to the point-like emission of ions from a single spot, the focusing to a beam with an ultra-small diameter is feasible. The adsorbtion of gas on the tip may be enhanced by cryostatic cooling of the tip. The focused ion beam may be used for a field ion This Taylor cone of liquid metal results in a very high electric field at the cone apex, which is required for field emission of the ions.

Fig. 2. Shape of the emitter tip coated with a liquid AuGe alloy (a) without Taylor cone; (b) with Taylor cone.

Reprinted with permission from Driesel W., Dietzsch C. & Muhle R., 1969. In situ observation of the tip shape of AuGe liquid alloy ion sources using a high volt transmission electron microscope. JVST B 14(5), 3367. Copyright 1969, American Vacuum Society..

The ion beam is used for imaging (Orloff et al., 1996), local implantation (Schmidt et al., 1997), physical milling (Giannuzzi & Stevie, 1999), gas-assisted etching (Utke et al., 2008), localized deposition (Matsui et al., 2000) and for exposure of resist layers (J. Melngailis, 1993) (Lee & Chung, 1998) as extensively described in literature (Tseng, 2005); (Giannuzzi & Stevie, 1999) (Jeon et al., 2010) (Tseng, 2004) and is therefore not further discussed here in detail.

### **3.3 He ion microscope**

'Heavy' ions, such as Ga+, may displace and scatter atoms in the substrate so much that device performance suffers. The He ion beam offers a new alternative. Helium ions are more massive than electrons by over three orders of magnitude and thus diffract less around apertures. Thus, smaller apertures are possible in a helium ion column than in an electron column, and this enables a smaller spot size. The specied spot size for a Zeiss Orion Plus helium ion microscope is 0.75 nm at an accelerating voltage of 30 kV. The first commercial helium ion microscope was introduced in 2006 (B. W. Ward et al., 2006) and by now has reached a maturity so that edge resolutions of <0.35 nm have become routinely possible.

As ion source a cryogenically cooled metal needle with a tip in the shape of a three-sided pyramid is used. The He+ source can be cooled to around 80 K, which resembles a point source that can be focused. When gun temperature exceeds 95 K, this structure is unstable, meaning source size and thus brightness may become compromised at higher temperatures A small quantity of helium is admitted in the vicinity of the sharp tip in the shape of a threesided pyramid. The apex of the pyramid consists of a set of three atoms, the trimer. The injected helium is then polarized by the large electric field and He atoms accelerate towards ionization area near the three topmost atoms. Only in this restricted area at the pyramidal tip does ionization take place. The charged He ions from one emitter atom are selected and are accelerated into the ion column to produce the focused electron beam. The ion optics should theoretically operate around unity magnication.

Focused Ion Beam Lithography 35

smaller structures. He ion microscopy is highly suitable for imaging of insulating samples and biological samples. The scanning helium ion microscope can also be used for diffraction imaging in transmission mode (J. Notte 4th et al., 2010). This way, crystallographic information can be provided in the form of thickness fringes and dislocation images. This mode allows the recording of high-contrast images of crystalline materials and crystal

Helium ion microscopy has already been successfully used for resist-based structuring and the feasibility of 6nm features has been demonstrated (Sidorkin et al. 2009). Ion beams may also be used for sample sputtering, but the light He ions have a very low yield. Yet, successful milling of graphene structures by He ion microscopes has been shown by R. Hill & Faridur Rahman (2010) and Bell et al. (2009). As with Ga ion microscopy the ion beam may also be used for gasassisted deposition or etching. The fabrication of a W pillar with an average diameter of 50 nm grown by deposition in the He ion microscope has been demonstrated. This deposited pillar was 6.5 µm high and had a height to width aspect ratio of 130:1 (R. Hill & Faridur Rahman 2010). Also 10 nm wide nanowires have been deposited and sub-10 nm cuts in Au have been

The development of ion microscopes with heavier noble gas ions is currently underway (Livengood et al., 2011). Utilizing neon ions extends the capabilities of high-source brightness technology. The neon ion source will also use the trimer-gas-field ion source used

For a stable GFIS source it is necessary that other gas contaminants have lower ionization energy than the noble gas ions, otherwise ionization of contaminants might also occur. The resulting contamination of the source region would contaminate the trimer trip region. Besides helium (24.5 eV), neon (21.6 eV) is the only noble gas with an ionization energy significantly higher than that of contaminants such as O, (13.7 eV), N (14.5 eV) and CO2 (13.8

With a test system the beam diameter was determined to be 1.5 nm at 28 kV, with a sputter yield around 1 atom per incident ion for Si and 4 atoms per incident ion for Cu. In comparison to a gallium FIB this is by a factor of 2x lower. In comparison to the light helium

Nanomachining tests performed in a 600 nm SiO2-CDO dielectric stack and in 30 nm Cr– SiO2 using 24 kV beam energies (1 pA beam current) have achieved smallest via a 40 nm at the mid-point and 30 nm at the base, with a depth of 240 nm (6:1 aspect ratio via). These first results indicate structure widths larger than expected and side wall profiles poorer than expected, so that further improvements have to be implemented. The benefit of a Ne ion beam will be in the field of milling, as the heavier ion species is more suitable for material

From an industrial viewpoint, a major deficit of focused ion beam systems is the sequential scanning with a single beam resulting in a very low sample throughput. For this reason projection systems have been developed using a stencil mask (Hirscher et al., 2002). A broad helium beam is extracted from a plasma source. An ExB mass lter selects only the desired He ion species. The ion projection lithography (IPL) system uses electrostatic ion optics for

eV). Therefore, Ar (15.8 eV) Kr and Xe (11.1 eV) are less suitable ions for this process.

modication such as ion milling or beam-induced deposition or etching.

performed with a focused helium ion beam (Livengood et al. 2011)

defects even at modest beam energies.

**3.4 Ne ion microscope** 

in the He ion microscope.

ions this is by a factor of 100x higher.

**3.5 Ion projection systems** 

Fig. 3. Field ion microscope in its simplest form consists of a cryogenically cooled tip, biased to a high voltage. When the imaging gas is admitted, a pattern is visible on the scintillator. Reprinted with permission from Ward B.W., Notte J.A. & Economou N.P., 2006. Helium ion microscope: A new tool for nanoscale microscopy and metrology. JVST B 24(6), 2871. Copyright 2006, American Vacuum Society.

Fig. 4. Spherical tip after the atoms have been rearranged to form a three-sided pyramid. Now the ionization disks exist only over the topmost three atoms.

Reprinted with permission from Ward B.W., Notte J.A. & Economou N.P., 2006. Helium ion microscope: A new tool for nanoscale microscopy and metrology. JVST B 24(6), 2871. Copyright 2006, American Vacuum Society.

The depth of eld with a He ion microscope is correspondingly ve times larger as the convergence angle is typically ve times smaller than an SEM. Also the diffraction curve is over two orders of magnitude smaller compared to the SEM. Consequently, an ideally focused spot may have a spot size down to 0.25 nm.

With current systems, the virtual source size is smaller than 0.25 nm while providing a brightness of approximately 109 Acm-2. Measurements have shown an angular beam intensity of 0.5–1 µAsr-1 and an energy spread of 1 eV. (R. Hill & Faridur Rahman, 2010).

The interaction of the He ion beam with the sample is signicantly different than with either an electron beam or a Ga+ ion beam. Versus using electrons, He ions are advantageous by the strongly reduced diffraction effect which enables a tremendously increased resolution of

Fig. 3. Field ion microscope in its simplest form consists of a cryogenically cooled tip, biased to a high voltage. When the imaging gas is admitted, a pattern is visible on the scintillator. Reprinted with permission from Ward B.W., Notte J.A. & Economou N.P., 2006. Helium ion microscope: A new tool for nanoscale microscopy and metrology. JVST B 24(6), 2871.

Fig. 4. Spherical tip after the atoms have been rearranged to form a three-sided pyramid.

Reprinted with permission from Ward B.W., Notte J.A. & Economou N.P., 2006. Helium ion microscope: A new tool for nanoscale microscopy and metrology. JVST B 24(6), 2871.

The depth of eld with a He ion microscope is correspondingly ve times larger as the convergence angle is typically ve times smaller than an SEM. Also the diffraction curve is over two orders of magnitude smaller compared to the SEM. Consequently, an ideally

With current systems, the virtual source size is smaller than 0.25 nm while providing a brightness of approximately 109 Acm-2. Measurements have shown an angular beam intensity of 0.5–1 µAsr-1 and an energy spread of 1 eV. (R. Hill & Faridur Rahman, 2010). The interaction of the He ion beam with the sample is signicantly different than with either an electron beam or a Ga+ ion beam. Versus using electrons, He ions are advantageous by the strongly reduced diffraction effect which enables a tremendously increased resolution of

Now the ionization disks exist only over the topmost three atoms.

Copyright 2006, American Vacuum Society.

Copyright 2006, American Vacuum Society.

focused spot may have a spot size down to 0.25 nm.

smaller structures. He ion microscopy is highly suitable for imaging of insulating samples and biological samples. The scanning helium ion microscope can also be used for diffraction imaging in transmission mode (J. Notte 4th et al., 2010). This way, crystallographic information can be provided in the form of thickness fringes and dislocation images. This mode allows the recording of high-contrast images of crystalline materials and crystal defects even at modest beam energies.

Helium ion microscopy has already been successfully used for resist-based structuring and the feasibility of 6nm features has been demonstrated (Sidorkin et al. 2009). Ion beams may also be used for sample sputtering, but the light He ions have a very low yield. Yet, successful milling of graphene structures by He ion microscopes has been shown by R. Hill & Faridur Rahman (2010) and Bell et al. (2009). As with Ga ion microscopy the ion beam may also be used for gasassisted deposition or etching. The fabrication of a W pillar with an average diameter of 50 nm grown by deposition in the He ion microscope has been demonstrated. This deposited pillar was 6.5 µm high and had a height to width aspect ratio of 130:1 (R. Hill & Faridur Rahman 2010). Also 10 nm wide nanowires have been deposited and sub-10 nm cuts in Au have been performed with a focused helium ion beam (Livengood et al. 2011)

### **3.4 Ne ion microscope**

The development of ion microscopes with heavier noble gas ions is currently underway (Livengood et al., 2011). Utilizing neon ions extends the capabilities of high-source brightness technology. The neon ion source will also use the trimer-gas-field ion source used in the He ion microscope.

For a stable GFIS source it is necessary that other gas contaminants have lower ionization energy than the noble gas ions, otherwise ionization of contaminants might also occur. The resulting contamination of the source region would contaminate the trimer trip region. Besides helium (24.5 eV), neon (21.6 eV) is the only noble gas with an ionization energy significantly higher than that of contaminants such as O, (13.7 eV), N (14.5 eV) and CO2 (13.8 eV). Therefore, Ar (15.8 eV) Kr and Xe (11.1 eV) are less suitable ions for this process.

With a test system the beam diameter was determined to be 1.5 nm at 28 kV, with a sputter yield around 1 atom per incident ion for Si and 4 atoms per incident ion for Cu. In comparison to a gallium FIB this is by a factor of 2x lower. In comparison to the light helium ions this is by a factor of 100x higher.

Nanomachining tests performed in a 600 nm SiO2-CDO dielectric stack and in 30 nm Cr– SiO2 using 24 kV beam energies (1 pA beam current) have achieved smallest via a 40 nm at the mid-point and 30 nm at the base, with a depth of 240 nm (6:1 aspect ratio via). These first results indicate structure widths larger than expected and side wall profiles poorer than expected, so that further improvements have to be implemented. The benefit of a Ne ion beam will be in the field of milling, as the heavier ion species is more suitable for material modication such as ion milling or beam-induced deposition or etching.

#### **3.5 Ion projection systems**

From an industrial viewpoint, a major deficit of focused ion beam systems is the sequential scanning with a single beam resulting in a very low sample throughput. For this reason projection systems have been developed using a stencil mask (Hirscher et al., 2002). A broad helium beam is extracted from a plasma source. An ExB mass lter selects only the desired He ion species. The ion projection lithography (IPL) system uses electrostatic ion optics for

Focused Ion Beam Lithography 37

Fig. 6. SEM views of a dot array with 12.5 nm half-pitch features. HSQ was developed in

This approach has been successfully used to pattern high-resolution patterns with 12.5 nm half-pitch in inorganic HSQ resist and to replicate this pattern by nanoimprint lithography

Lithography is employed to define patterns inside a target material. Using an FIB, a multitude of processing techniques exists to achieve this goal. Similar to photolithography it can be achieved by exposing a resist material using the ion beam. However, with ions, patterns can also be defined by physically sputtering the target atoms (FIB milling), by triggering chemical reactions inside an adsorbed layer of a precursor gas (gas-assisted processing) and by ion

Among these techniques the most prominent are FIB milling and gas-assisted processing. They are employed for optical mask repair (Yasaka et al., 2008), circuit editing (CE) (Boit et al., 2008), transmission electron microscope (TEM) sample preparation and rapid prototyping (Persson et al., 2010). We will discuss these techniques only briefly since they are already well described and reviewed elsewhere (Reyntjens & Puers, 2001) (Utke et al.,

In the following sections we will review the work carried out on resist-based IBL and discuss the reasons for its failure as well as its chance of resurrection. Further we will present our findings on patterning using ion implantation with a focus on 3D nano patterning. Finally, we will introduce a new technique, called direct hard mask patterning (DHP) which combine the

When an ion hits the target, surface elastic and inelastic scattering processes will take place. While inelastic processes are responsible for the generation of photons and secondary electrons, elastic scattering will transfer kinetic energy from the ion to the target atoms (Orloff et al., 2002). This kinetic energy transfer will cause the displacement of the target

2008). Instead we will focus on the less prominent FIB patterning techniques.

advantages of FIB milling with the speed of resist-based lithography.

**4.1 FIB milling and gas-assisted processing** 

Reprinted from Publication Muehlberger M. et al, Nanoimprint lithography from CHARPAN Tool exposed master stamps with 12.5 nm hp, Microel. Eng. 88/8 2070,

NaOH/NaCl. The scale bar is 400 nm.

(Muehlberger et al., 2011)

**4. Lithography** 

implantation.

Copyright 2010, with permission from Elsevier.

reduction printing of stencil mask patterns to a magnication factor of 4. Monitoring the position of the ion beam for correction of the projected image was achieved with a pattern lock system which consists of (i) detectors measuring the position of beamlets, (ii) transputer-based controllers and (iii) beam control elements.

An ion projection lithography system for exposure of the Shipley XP9946 resist family allowing for very high resolution of 50 nm was developed. A high pattern collapse probability was experienced at high aspect ratios. Required ion doses varied with the composition of the resist and were in the range of 1.4 down to 0.12 µC/cm². Alternatively sensitivity adjustment by a variation of the photo acid generator (PAG) was achieved.

### **3.6 Multi-beam systems**

Based on an ion projection concept using a stencil mask, further development efforts of IMS Nano have brought forward an ion multi-beam system. This multi-beam system features a programmable aperture plate with integrated CMOS electronics (Hans Loeschner et al., 2010). This aperture plate is equipped with deflection electrodes and a blanking plate. A beam deection of 300 mrad from the axis is sufficient to lter out a beamlet. By blanking through one aperture a single beam can be individually switched on and off. The produced pattern of individually switched ion beams can be demagnified leading to a 200x pattern reduction.

As ion source a broad beam generated from plasma was used. The gases ionized ranged from hydrogen H3+ to Argon (Koeck et al., 2010).

Using 10 keV H+ ions, a 20 nm thick layer of the inorganic photoresist hydrogen silsesquioxane (HSQ) was exposed. For this purpose the sample was irradiated by 43.000 beams with exposure dose of 12 mC/cm2. Tetramethylammonium hydroxide (TMAH) was used for resist development. After development, an effective 15 nm half-pitch (hp) resolution in 50 nm HSQ resist could be confirmed (Hans Loeschner et al., 2010). Development in NaOH/NaCl required a 3.3x higher exposure dose but longer exposure led to reduced shot noise inuence on line edge roughness (LER).

Fig. 5. Schematics of a 43k-APS unit of the IMS system providing 43 thousand programmable beams.

Reprinted with permission from Loeschner Hans, Klein C. & Platzgummer Elmar, 2010. Projection Charged Particle Nanolithography and Nanopatterning. JJAP, 49(6), 06GE01..

reduction printing of stencil mask patterns to a magnication factor of 4. Monitoring the position of the ion beam for correction of the projected image was achieved with a pattern lock system which consists of (i) detectors measuring the position of beamlets, (ii)

An ion projection lithography system for exposure of the Shipley XP9946 resist family allowing for very high resolution of 50 nm was developed. A high pattern collapse probability was experienced at high aspect ratios. Required ion doses varied with the composition of the resist and were in the range of 1.4 down to 0.12 µC/cm². Alternatively sensitivity adjustment by a variation of the photo acid generator (PAG) was achieved.

Based on an ion projection concept using a stencil mask, further development efforts of IMS Nano have brought forward an ion multi-beam system. This multi-beam system features a programmable aperture plate with integrated CMOS electronics (Hans Loeschner et al., 2010). This aperture plate is equipped with deflection electrodes and a blanking plate. A beam deection of 300 mrad from the axis is sufficient to lter out a beamlet. By blanking through one aperture a single beam can be individually switched on and off. The produced pattern of individually switched ion beams can be demagnified leading to a 200x pattern reduction. As ion source a broad beam generated from plasma was used. The gases ionized ranged

Using 10 keV H+ ions, a 20 nm thick layer of the inorganic photoresist hydrogen silsesquioxane (HSQ) was exposed. For this purpose the sample was irradiated by 43.000 beams with exposure dose of 12 mC/cm2. Tetramethylammonium hydroxide (TMAH) was used for resist development. After development, an effective 15 nm half-pitch (hp) resolution in 50 nm HSQ resist could be confirmed (Hans Loeschner et al., 2010). Development in NaOH/NaCl required a 3.3x higher exposure dose but longer exposure led to reduced shot noise inuence on line

Fig. 5. Schematics of a 43k-APS unit of the IMS system providing 43 thousand

Reprinted with permission from Loeschner Hans, Klein C. & Platzgummer Elmar, 2010. Projection Charged Particle Nanolithography and Nanopatterning. JJAP, 49(6), 06GE01..

transputer-based controllers and (iii) beam control elements.

from hydrogen H3+ to Argon (Koeck et al., 2010).

**3.6 Multi-beam systems** 

edge roughness (LER).

programmable beams.

Fig. 6. SEM views of a dot array with 12.5 nm half-pitch features. HSQ was developed in NaOH/NaCl. The scale bar is 400 nm.

Reprinted from Publication Muehlberger M. et al, Nanoimprint lithography from CHARPAN Tool exposed master stamps with 12.5 nm hp, Microel. Eng. 88/8 2070, Copyright 2010, with permission from Elsevier.

This approach has been successfully used to pattern high-resolution patterns with 12.5 nm half-pitch in inorganic HSQ resist and to replicate this pattern by nanoimprint lithography (Muehlberger et al., 2011)
