Other Resists Archives - Allresist EN https://www.allresist.com/category/resist-wiki/resist-wiki-e-beam-resist/wiki-e-beam-resist-other-resists/ ALLRESIST GmbH - Strausberg, Germany Wed, 27 Jul 2022 10:50:00 +0000 en-GB hourly 1 https://wordpress.org/?v=6.5.2 Poly(phthalaldehyde)-based electron beam resists, University of Tübingen https://www.allresist.com/polyphthalaldehyde-based-electron-beam-resists-university-of-tubingen/ Wed, 27 Jul 2022 10:20:51 +0000 https://www.allresist.com/?p=17674 A direct positive patterning of PPA layers is possible by electron bombardment. Similar to the irradiation of normally used e-beam resists like e.g. CSAR 62 or PMMA, the electron beam causes a fragmentation of the polymer chains.

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Poly(phthalaldehyde)-based electron beam resists, University of Tübingen

A direct positive patterning of PPA layers is possible by electron bombardment. Similar to the irradiation of normally used e-beam resists like e.g. CSAR 62 or PMMA, the electron beam causes a fragmentation of the polymer chains. The polymer fragments produced from poly(phthalaldehydes) are however instable and disintegrate directly into the volatile monomers. In this process, only extremely small amounts of monomeric phthalaldehydes are released which do not significantly influence the quality of the applied vacuum and can furthermore be exhausted completely. Approximately 2×10-6 ng (only 2 femtogram!) of phthalaldehyde is for example released during the writing of a trench with a length of 1000 nm and a width of 50 nm at a film thickness of 30 nm. By selective overexposure, also lift-off architectures can be generated due to the associated proximity effect.

First experiments concerning a direct structuring by e-beam irradiation have already been carried out at the Raith company. Using the (not yet finally optimised) PPA resist samples of the SX AR-P 8100 series on a PMMA layer, an almost complete development can be achieved with a dose of only about 5 μC/cm² (2 kV). At an acceleration voltage of 30 kV, the value is approx. 35 μC/cm². Substrates which are ejected from the e-beam device after exposure are already completely developed.

Belichtungsraster

Figure: Exposure grids with acceleration voltage and dose variations.

Scanprofil

Figure: Scan profile determined on a Dektak 150 profilometer; depth of development as a function of the dose, exemplarily demonstrated for an acceleration voltage of 10 kV.

With increasing exposure dose, also concurrent crosslinking processes are becoming more and more important. Radicals produced by the electron beam are able to stabilize crosslinks and consequently also the layer. This effect likewise occurs with PMMA, even though at much higher exposure doses, and is here used to create negative PMMA architectures.

To determine the resolution limits of resist sample SX AR-P 8100, the company Raith investigated lines patterns in detail. Lines of variable width were written into the PPA layer and coated with a thin platinum layer after metallisation (sputter coating, about 4 nm platinum layer). Line widths of about 20 nm could reliably be produced, and the highest resolution obtained so far was 16 nm.

Linien-in-PPA-geschrieben

Figure: Lines written into PPA (resist SX AR-P 8100).

16nm-Steg-nach-Sputtercoating-mit-Platin

Figure: 16-nm bar obtained after sputter coating with platinum.

Overview E-beam Other Resists



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]]> PPA for two layer applications https://www.allresist.com/ppa-for-two-layer-applications/ Tue, 22 Mar 2022 10:12:11 +0000 https://www.allresist.com/?p=17003 Report on the two layer system, respectively lift-off: AR P-617 (250nm) with PPA (30nm), development followed by vapor coating of Al (40nm).

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PPA for two layer applications

Report on the two layer system, respectively lift-off:

AR P-617 (250nm) with PPA (30nm), development followed by vapor coating of Al (40nm). (5% H2O in IPA resulted in development rate of 0.5 nm/sec.)

– Development rate of AR-P 617 can be adjusted precisely by means of  the water concentration in IPA (5 -10% corresponding to 0,5 – 2,5 nm/s)

Dependence of the development rate of AR-P 617 in developers with variable water concentration in IPA, 21°C, SB 5′ 180°C

– used very successfully for the production of undercut structures

Bridge with undercut, covered by 40 nm aluminum

Developer:

  • 10 w-% of DI-water in IPA
  • Stirring!
  • Used 130 seconds, which is a 30% overetch
  • Evaporation of 40 nm Aluminum. Unfortunately, the layer is quite stressful and it peeled of around the cleaving edge

Results:

  • Undercut is nicely visible, bridge is 100 nm wide, which leads to an undercut of 160 nm ([420-100]/2)
  • Metal on the silicon was detached during the cleaving.
  • At the test structure one can nicely see the residuals in the fields. Most residuals remain for the widest cap, while all caps flew away because they were fully underetched.

Overview E-beam Other Resists



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]]> CAR 44 for e-beam lithography https://www.allresist.com/car-44-fuer-die-e-beam-lithographie/ Fri, 12 Oct 2018 12:07:57 +0000 https://www.allresist.de/?p=7011 We now succeeded in finding a remarkable solution for high-layer e-beam structuring. The negative resist CAR 44 (AR-N 4400-10) was coated to yield a layer with a height of 9.5 μm, dried, and irradiated.

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CAR 44 for e-beam lithography

Layer thicknesses of more than 5 μm are rarely required for electron beam lithography, and consequently only isolated attempts have been made to pattern PMMA layers up to a layer thickness of 20 μm by electron beam exposure. The PMMA e-beam resist AR-P 6510 is suitable for this purpose, but special developers (AR 600-51) and stoppers (AR 600-61) are needed for the subsequent development. If conventional MIBK/isopropanol developers are used, the layer will in most cases crack during the development step.
We now succeeded in finding a remarkable solution for high-layer e-beam structuring. The negative resist CAR 44 (AR-N 4400-10) was coated to yield a layer with a height of 9.5 μm, dried, and irradiated.
At a dose of about 40 μC/cm² (100 kV), 2 μm wide lines were written, cross-linked at 105 °C and developed with developer AR 300-26.

2 µm lines generated by e-beam lithography in a layer with a thickness of 9.5 µm

Even layers with higher film thicknesses can be structured. CAR 44 is thus also suitable as electron beam resists for this kind of applications.


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]]> Atlas 46 for e-beam lithography https://www.allresist.com/resist-wiki-atlas-46-for-e-beam-lithography/ Fri, 12 Oct 2018 12:06:07 +0000 https://www.allresist.de/?p=7008 A new application field for Atlas 46 is electron beam lithography, as experiments with a thin Atlas resist layer patterned by e-beam lithography demonstrated. At a layer thickness of 450 nm, 200 nm lines were written into this layer. The sensitivity was 70 μC/cm² at an acceleration voltage of 100 kV.

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Atlas 46 for e-beam lithography

A new application field for Atlas 46 is electron beam lithography, as experiments with a thin Atlas resist layer patterned by e-beam lithography demonstrated. At a layer thickness of 450 nm, 200 nm lines were written into this layer. The sensitivity was 70 μC/cm² at an acceleration voltage of 100 kV. The solvent-based development was carried out with AR 300-12, followed by a short post treatment with acetone.

200 nm lines generated with Atlas resist

Atlas 46 is thus also suitable for a use as electron beam resist.


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]]> Phoenix 81 – Storage conditions and dispatch https://www.allresist.com/resist-wiki-phoenix-81-storage-conditions-and-dispatch/ Mon, 09 Jul 2018 07:52:51 +0000 https://www.allresist.de/?p=6891 In the final stage of the Eurostar PPA-Litho project which was aimed to develop the resist Phoenix, we achieved to generate far more stable PPA polymers by optimizing the synthesis procedure. Pure polyphthalaldehydes which were subjected to a “stress test” for 14 days at 37 °C showed no decomposition. These resists can thus be shipped without cooling; this however only applies to pure PPA polymers.

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Phoenix 81 – Storage conditions and dispatch

The various possible applications of Phoenix 81 have already been reported on in the Resist Wiki (see PPA resists). Due to their easily inducible thermal decomposition (see principle of NanoFrazor technology), resist solutions in anisole were so far not long-term stable. In order to ensure a shelf life of 6 months, a storage temperature of -18 °C was recommended. If the resist or dry polymers were kept at room temperature, decomposition started within a few days. The delivery to customers was consequently difficult and costly (within Europe, a transport in dry ice at -78.5 °C is charged with about € 200; expenses for air freight can be far beyond € 1,000).

In the final stage of the Eurostar PPA-Litho project which was aimed to develop the resist Phoenix, we achieved to generate far more stable PPA polymers by optimizing the synthesis procedure.

To evaluate the stability, PPA (powder) samples were filled into different sample vials and stored for 4 weeks under different conditions, e.g. in the freezer at -18 °C or at room temperature (reference temperature is the recommended storage temperature of -18 °C). Selected PPA samples were furthermore daily heated to 35-36 °C for about 8 to 9 hours over a period of 1.5 and 4 weeks, respectively. Subsequently, 5.5 % solutions of the stored PPA samples in anisole were prepared and coated at 2000 rpm. After a soft-bake (3 minutes at 95 °C on the hotplate), the layer thicknesses were determined using a profilometer.

Measurement of PPA film thickness before and after tempering

For all stored samples, identical layer thicknesses within the error accuracy were measured which indicates that, even at higher temperatures, samples show no signs of decomposition just like the PPA which was optimally stored at -18 °C. The PPA thus passed the „stress test“; a cheaper delivery without cooling is easily possible.

The high stability of the PPA powder and the low-cost shipping prompted us to offer Phoenix 81 in the future as a solid by the gram. Upon request, we can also supply the resist solvent (anisole) and a filtration tip as part of a set.

Overview E-beam Other Resists



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]]> Fluorescent resist structures https://www.allresist.com/resist-wiki-fluorescent-resist-structures/ Wed, 11 Oct 2017 14:37:51 +0000 https://www.allresist.de/?p=6558 Fluorescence is the spontaneous emission of light briefly after a substance is excited by electronic transitions. The emitted light has usually less energy than the previously absorbed light.

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Fluorescent resist structures

Fluorescence is the spontaneous emission of light briefly after a substance is excited by electronic transitions. The emitted light has usually less energy than the previously absorbed light.

Figure 1: Absorption and emission spectra

Figure 1 shows that the fluorescence (emission) is long-wave (less energetic) than the excitation by absorption.

This is documented nicely in the resist structures of the new fluorescent e-beam resist. For the production of the new resists, both PMMA and CSAR 62 polymers were prepared in a solvent mixture which also dissolved the fluorescence dyes to a sufficiently high degree. These resists were then irradiated and developed at the company Precision Optics Gera GmbH using electron beam lithography. The structures could be generated residue-free in a developer optimised for this purpose. If excited by UV light as shown in the two pictures, they begin to fluoresce brightly.

Figure 2: Fluorescent PMMA structures yellow-green

Figure 3: Fluorescent PMMA structure red

Due to the properties of these e-beam resists are resolutions down to the range of 10 – 20 nm possible. The focus of the applications is in the optical industry; these materials are e.g. required for night vision devices.

Figure 4: Poster MNE 2017

Overview E-beam Other Resists



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]]> Top Surface Imaging E-Beamresist https://www.allresist.com/top-surface-imaging-e-beamresist/ Fri, 03 Feb 2017 12:35:15 +0000 https://www.allresist.de?p=6370 The DESIRE process can also be used for electron beam lithography even though certain differences exist between photo and e-beam lithography. Structures are written into the resist layer by means of electrons.

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]]> The DESIRE process (see Wiki “Top surface imaging photoresist”) can also be used for electron beam lithography even though certain differences exist between photo and e-beam lithography. Structures are written into the resist layer by means of electrons. The components (novolacs and LSCs) intensively crosslink and the OH groups of the novolacs thus remain protected. Naphthoquinone diazide (LSC) is not converted into indene carboxylic acid (see Wiki 1.xxx) during exposure, which is due to the high vacuum during irradiation that removes water from the layer. Water is however a mandatory reaction partner for the conversion into indene carboxylic acid. After partial crosslinking, the resist layer is flood-exposed by photolithography (300-450 nm wavelength). Indene carboxylic acid is again formed in previously unexposed areas and the protective effect on the OH groups of the novolac is released. The organosilicon component (e.g. HMDS) is now able to penetrate into the layer at these sites. If then a dry development with oxygen plasma is performed, the electron-irradiated, non-silylated structures are removed and a positive e-beam resist results.

Within the scope of the BMBF project FB (01 M 2854 D) July 1995 “Electron beam direct writing for submicrometre ASICs” (Institute for Semiconductor Physics, Frankfurt/O., Allresist GmbH), the process was extended insofar that a structuring photolithography was carried out instead of a flood exposure. Areas not exposed during photolithography are also removed in oxygen plasma. A mix & match technology between e-beam and photolithography is thus now available to users. The specific process steps are shown in Figure x:

TSI-Prozessschema

Fig. 1 Process steps of the TSI e-beam lithography procedure

The advantages of the TSI procedure develop their full potential during e-beam lithography especially if very small acceleration voltages (1 – 5 kV) are used. At 1 kV, electrons penetrate only 150 nm deep into the resist layer due to the low acceleration voltage. The energy input entirely remains in the layer. The low penetration depth is completely sufficient for the TSI process.

Eindringtiefen-der-Elektronen-in-Resistschicht

Fig. 2 penetration depths of the electrons in the resist layer dependent on acceleration stress

The penetration depth of the silylation process can easily be checked. The silylated novolac is readily soluble in nonpolar, aromatic solvents (e.g. toluene or xylene) while the unsilylated resist is insoluble in these solvents. If a “development” in toluene is carried out, the silylated resist layer can be dissolved out.

Toluenbehandlung

Fig. 3 shows bars with a width of 1 µm written by e-beam (1.8 kV), followed by flood-exposure and silylation for a longer period of time. The silylated novolac is completely washed out during the “development” with toluene, and only the bridges which were crosslinked by e-beam exposure remain standing.

Allresist also developed a TSI e-beam resist. The experimental model SX AR-P 7300/8 is a positive electron beam resist based on safer solvents which works according to the principle of top surface imaging (modified DESIRE process). After the structuring electron irradiation, the resist is subjected to a flood exposure in the range of 300-450 nm and a surface silylation. The development is carried out in oxygen plasma. The silylated resist is oxidised to form a SiOx mask which is used to transfer the structure into the underlying layer. Mix & match applications are possible; i.e. after electron irradiation, UV exposure and subsequent development with RIE-O2 follow in one step.

The handling process comprises the following steps:

• Coating

• Tempering (softbake)

• Electron irradiation

• Flood exposure

• Silylation from the gas phase

• Dry development (O2 plasma)

As an alternative to gas phase silylation, a liquid silylation can be used.

In the case of mix & match applications, a structuring UV lithography is used instead of flood exposure, but both processes have to be coordinated carefully.

Resiststrukturen

Strukturen

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]]> PMMA lift-off structures on semi-precious stone substrates using Electra 92 https://www.allresist.com/resist-wiki-pmma-lift-off-structures-on-semi-precious-stone-substrates-using-electra-92/ Mon, 05 Oct 2015 07:24:51 +0000 https://www.allresist.de?p=5358 Semi-precious stones like sapphire or garnet increasingly gain in importance as substrates for semiconductor industry. Even though these materials have insulating properties, a patterning with electron beam lithography is nevertheless possible with the help of Electra.

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PMMA lift-off structures on semi-precious stone substrates using Electra 92

Semi-precious stones like sapphire or garnet increasingly gain in importance as substrates for semiconductor industry. Even though these materials have insulating properties, a patterning with electron beam lithography is nevertheless possible with the help of Electra. Mr. Chi Tang has been working since 2015 at the University of California with Electra 92. His specialty is the coating of PMMA on semi-precious stones such as garnet in a PMMA two-layer process. Since he started to work with AR-PC 5090.02 (former SX AR-PC 5000/90.2), he is able to easily process his lift-off structures with the two-layer system.

Lift-off-Strukturen-auf-Granat-mit-Electra92

Lift-off structures on garnet supported by Electra 92

Overview E-beam Other Resists



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]]> Electra 92 variant optimised for applications on novolac-based resists https://www.allresist.com/resist-wiki-electra-92-variant-optimised-for-applications-on-novolac-based-resists/ Mon, 05 Oct 2015 07:20:09 +0000 https://www.allresist.de?p=5354 Novolac-based e-beam resists have other surface properties than e.g. CSAR 62, PMMA, or HSQ resists. Due to a higher solvent content of the conductive resist as for example is the case with SX AR-PC 5000/90.2, these novolac-resists are already moderately attacked.

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Electra 92 variant optimised for applications on novolac-based resists

Novolac-based e-beam resists have other surface properties than e.g. CSAR 62, PMMA, or HSQ resists. Due to a higher solvent content of the conductive resist as for example is the case with  AR-PC 5090.02, these novolac-resists are already moderately attacked. Therefore, AR-PC 5091.02 was designed which is characterised by improved coating properties for the coating of e-beam resists such as AR-N 7520, AR-N 7700, or AR-P 7400.

60-150nm-Quader-AR-N7700.08-auf-Glas

60 – 150 nm squares of AR-N7700.08 (100 nm height) on glass

AR-N 7700.08 as shown in the figure was spin-deposited on glass, dried, coated with SX AR-PC 5000/91.1, and baked at 50 °C. After exposure, the Electra 92 layer was removed with water (2 x 15 seconds) and the e-beam resist subsequently developed. This resulted in a resolution of approximately up to 60 nm which is a very good value for a chemically enhanced resist. However, this high solution required a high dose of approx. 1.000 µC/cm² as well as a strong developer (AR 300-26).

Overview E-beam Other Resists



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]]> Conductivity under the application conditions of e-beam lithography https://www.allresist.com/resist-wiki-conductivity-under-the-application-conditions-of-e-beam-lithography/ Mon, 05 Oct 2015 07:14:07 +0000 https://www.allresist.de?p=5350 The measured conductivity of resist layers is strongly influenced not only by the temperature but also directly dependent on the air humidity. After a softbake, the now almost anhydrous layer gradually takes up water at room temperature from the ambient air due to the slightly hygroscopic properties of the polymer.

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Conductivity under the application conditions of e-beam lithography

The measured conductivity of resist layers is strongly influenced not only by the temperature but also directly dependent on the air humidity. After a softbake, the now almost anhydrous layer gradually takes up water at room temperature from the ambient air due to the slightly hygroscopic properties of the polymer. The measured resistance increases significantly. In order to assess the conductivity properties of Electra 92 under the conditions of e-beam lithography, Mr. Riebe (University of Potsdam) conducted corresponding measurements in a high vacuum. In these tests, Electra 92 was coated on quartz plates (film thickness about 190 nm), the polymer film contacted with clamps, and the measurement arrangement transferred into a vacuum chamber.

Messanordnung-Bestimmung-Leitfähigkeit

Measurement arrangement to determine the conductivity under vacuum conditions

Under atmospheric conditions, a resistance of > 21 MΩ was measured. The resistance decreased rapidly to 16.6 MΩ directly after applying the vacuum (2*10-3 Torr) and finally decreased further to about 12.7 MΩ (at 2*10-4 Torr). After ventilation, the measured resistance quickly increased again to 20 MΩ.

Interestingly, almost a doubling of the measured conductivity is observed in a vacuum (the resistance is accordingly halved). Under these conditions, the conductive layer is virtually anhydrous and thus shows a higher conductivity.

In e-beam applications with a much stronger vacuum consequently a conductivity of up to about 1 S/m can be assumed, which is completely sufficient for most applications.

Overview E-beam Other Resists



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