Miroslav Mihov

Negative resist image by dry etching: a novel surface imaging resist scheme

Top surface imaging (TSI) is an established technique that can be used to improve resolution in optical, ultraviolet and electron-beam lithography into the nanometer region. This paper describes a novel top surface imaging process, which incorporates ion-beam exposure, silylation and dry development, and can support nanometer resolution. The negative resist image by dry etching (NERIME) process is a TSI scheme for DNQ/novolak based resists and can result in either negative or positive resist image depending on the processing conditions. Results show that focused Ga+ ion-beam exposure with a dose in the range of 1-50 µC cm-2 at 30 keV can successfully prevent silylation of the resist, thus resulting in the formation of positive image after the dry etching. A negative image can be formed by using a second ion-beam exposure with a dose higher than 900 µC cm-2 at 30 keV to pattern lines into the original exposed resist area. The NERIME processed patterns down to 0.1 µm have been formed in Shipley SPR505A resist, and exhibit highly vertical sidewalls due to the ion-beam exposure and oxygen dry development. Results show that this novel TSI scheme could be successfully applied for fabrication of critical CMOS process steps, such as deep isolation trench formation and lithography over substantial topography.

Negative resist image by dry etching as a surface imaging process using focused ion beams

Focused ion beam (FIB) lithography has significant advantages over the electron beam counterpart in terms of resist sensitivity, backscattering, and proximity effects. However, combining the FIB lithography with top surface imaging (TSI) will extend its advantages by allowing anisotropic processing of thicker resist layers. This article reports the development of novel single layer lithography process by combining focused Ga+ ion beam (Ga+ FIB) lithography, silylation, and oxygen dry etching. The negative resist image by dry etching is a TSI scheme for DNQ/novolak based resists and can result in either positive or negative resist images depending on the extent of the ion beam exposure dose. Results show that the Ga+ ion beam dose in the range of 1–50 μC/cm2 at 30 keV can successfully prevent silylation of the resist, thus resulting in the formation of a positive image after the dry etching. A negative image can be formed by using a second Ga+ ion beam exposure with a dose higher than 900 μC/cm2 at 30 keV ...

Focused ion beam lithography-overview and new approaches

Focused Ion Beam (FIB) lithography has significant advantages over the electron beam counterpart in terms of resist sensitivity, backscattering and proximity effects. Applying the Top Surface Imaging (TSI) principal to FIB lithography could further enhance its capability. In this paper we review different FIB lithography processes which utilise both wet and dry development. As of further development of this technology, we report a novel lithography process which combines focused Ga/sup +/ ion beam (Ga/sup +/ FIB) exposure, silylation and oxygen dry etching. The Negative Resist Image by Dry Etching (NERIME) is a TSI scheme for DNQ/novolak based resists and can result in either positive or negative resist images depending on the extent of the ion beam exposure dose. The NERIME process can resolve nanometer resist patterns as small as 30nm yet maintaining high aspect ratio of up to 15. The proposed lithography scheme could be utilised for advanced prototype ICs fabrication and critical CMOS lithography process steps.

Two-step modified NERIME process using combined focused ion beam lithography and plasma etching

Focused ion beams (FIB) have been widely used as a patterning lithography technique for advanced ICs and optical masks fabrication. FIB lithography has certain advantages over the direct-write electron beam lithography in terms of resist sensitivity, backscattering and proximity effects. However, combining the FIB exposure with both Top Surface Imaging (TSI) and dry etching will further extend its advantages towards anisotropic processing of thicker resist layers in comparison to those used by the conventional lithography processes. The newly developed NERIME (Negative Resist Image by Dry Etching) process combines these advantages by the incorporation of focused Ga+ ion beam (Ga+ FIB) exposure, near UV exposure, silylation and dry etching. The work described here follows our investigations into the NERIME process for nanostructure applications and outlines a simplified (two-step) process incorporating FIB exposure and oxygen dry development. The two-step modified NERIME process is a negative working TSI system for DNQ/novolak based resists. Results show that Ga+ ion beam dose higher than 800μC/cm2 at 30keV can modify the exposed resist areas as to withstand the subsequent oxygen plasma etching, thus giving formation of negative resist image. In this study, nanometer resist patterns as small as 30nm with high aspect ratio of up to 15 were successfully resolved due to the high resolution ion beam exposure and anisotropic dry development. The proposed two-step lithography scheme could be utilized for the fabrication of critical CMOS process steps, such as sub-100nm gate formations and lithography over substantial topography.

Investigations of the Ga+ focused-ion-beam implantation in resist films for nanometer lithography applications

A focused-ion-beam (FIB) machine is a versatile tool used extensively in the IC industry for conducting failure analysis, prototype fabrication, and device repair. Lithography can also be performed by the FIB technique for direct patterning of photoresists, followed by wet or dry development. We studied how the property of resist regions changes during oxygen dry development in the NERIME (the negative-resist-image-by-dry-etching) process after subjecting to FIB-assisted gallium implantation. The NERIME process is a single-layer scheme, in which DNQ/Novolak-based resists are exposed by gallium ions with FIB, followed by near-ultraviolet flood exposure, silylation, and oxygen dry etching. This process can yield both positive and negative resist images. In addition, the NERIME technique can achieve a nanometer resolution down to 80nm and a high aspect ratio for the processed patterns. A scanning-transmission-electron-microscope (STEM) analysis of the resist regions FIB-implanted with gallium ions has reveal...

Negative resist image by dry etching as a novel top surface imaging process for ion-beam lithography

Focused Ion beam (FIB) lithography has significant advantages over the electron beam counterpart in terms of resist sensitivity, backscattering and proximity effects. However, combining the FIB lithography with Top Surface Imaging (TSI) will extend its advantages by allowing anisotropic processing of thicker resist layers. This paper reports the development of novel single layer lithography process by combining focused Ga+ ion beam (Ga+ FIB) lithography, silylation and oxygen dry etching. The Negative Resist Image by Dry Etching (NERIME) is a TSI scheme for DNQ/novolak based resists and can result in either positive or negative resist images depending on the extent of the ion beam exposure dose. Results show that Ga+ ion beam dose in the range of 1μC/cm2 to 50μC/cm2 at 30keV can successfully prevent silylation of the resist, thus resulting in the formation of positive image after the dry etching. A negative image can be formed by using a second Ga+ ion beam exposure with a dose higher than 900 μC/cm2 at 30keV to pattern lines into the original exposed resist area. It was observed that resist regions exposed to such high doses can effectively withstand oxygen dry development, thus giving formation of negative resist image. In this study, nanometer resist patterns with high aspect ratio up to 15 were successfully resolved due to the ion beam exposure and anisotropic dry development. This novel TSI scheme for ion beam lithography could be utilized for the fabrication of critical CMOS process steps, such as deep isolation trench formation and lithography over substantial topography.

Top surface imaging lithography processes for I-line resists using liquid-phase silylation

In this paper, liquid-phase silylation process for Top Surface Imaging Lithography systems incorporating e-beam exposure has been experimentally investigated using FT-IR spectroscopy, UV spectroscopy, SIM spectrometry and SEM cross-sectionals. The impact of different silylating agents on Shipley SPR505A resist system is presented for both the UV exposed and e-beam crosslinked regions of the resist. Results show that an e-beam dose of 50/spl mu/C/cm/sup 2/ at 30keV is sufficient to crosslink the resist and prevent silylation. The silylation contrast using HMCTS was found to be the highest (11:1) in comparison with other two agents. It was found that the silicon incorporation in SPR505A resist follows Case II diffusion mechanisms.

PRIME process with Shipley SPR505A resist—simulations and experiments

PRIME process with I-line Shipley SPR505A resist was investigated using both simulations and experiments. Modelling of the PRIME process steps for 50-nm lines/spaces grating and 30-nm single line is shown. The liquid-phase silylation step in PRIME with SPR505A resist was experimentally characterised using FT-IR spectroscopy, UV spectroscopy and SIM spectrometry. The silylation agent used was hexamethylcyclotrisiloxane. The results show case II diffusion behaviour of the silicon incorporation in the SPR505A resist. The silylation contrast of the process as determined by the ratio of the silicon uptake in the near UV exposed over e-beam crosslinked regions was found to be 5 to 1.

Modelling and simulations of nanostructures for Shipley SPR505A resist using PRIME process

The Positive Resist Image by dry Etching (PRIME) process is a high resolution lithography system incorporating electron beam exposure, silylation and dry development. The process steps in PRIME with Shipley SPR505A resist have been modeled and simulations of nanostructures (50nm lines/spaces, 30nm single line) has been presented. The silylation process step in PRIME with SPR505A resist has been experimentally characterized using FT-IR spectroscopy.

Nanostructure patterns for Shipley SPR505A resist using PRIME process

Top Surface Imaging (TSI) is a well-established technique to improve resolution for optical, ultraviolet (UV) and e-beam lithography. The Positive Resist Image by Dry Etching (PRIME) process is a high resolution single layer lithography system incorporating electron beam exposure, silylation and dry development. In this paper, modeling of nanostructures down to 30nm using PRIME with 0.5micrometers thick Shipley SPR505A resist are presented. The simulated profiles have been found to correlate closely with the published experimental data. Moreover, the liquid-phase silylation process step in PRIME has been experimentally characterised using FT-IR spectroscopy, UV spectroscopy, SIM spectrometry as well as cross-sectional SEM and TEM. The impact of different silylating agents on SPR505A is presented for both the UV exposed and e-beam crosslinked regions of the resist. Results show that an e-beam dose of 50(mu) C/cm2 at 30KeV is sufficient to crosslink the resist and prevent silylation. The silylation contrast using Hexamethylcyclotrisilazane (HMCTS) was found to be the highest (11:1) in comparison with other two silylating agents. It was found that the silicon incorporation in SPR505A resist follows Case II diffusion mechanisms.