Specific Process Knowledge/Lithography/EBL

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ebl e-beam writer e-beamwriter ebeamwriter e-beamlithography

Quick links

JEOL 9500 User Guide

My first JEOL 9500 exposure tutorial

JEOL cassette specifications

Beamer guide

Tracer guide

JEOL 9500 trouble shooting guide

Introduction to E-beam lithography at DTU Nanolab

DTU Nanolab has two E-beam writing systems, a JEOL JBX-9500 FSZ and a Raith eLINE Plus. The two systems are very different and new users should consult the EBL team to dertermine which system is appropriate for a particular project or type of sample. The general specifications of the two tools are given in the table below and may serve as a guideline for choice of system to use, especially the pros and cons list at the end of the table. Newcommers to EBL should start by watching our JEOL 9500 process video to see how a typical process is done.

Compared to UV lithography EBL is somewhat more complicated and in general a significantly longer process. Writing time (per area) is much higher and thus EBL is only adviseable for structures with Critical Dimensions (CD) below 1 µm. For CD equal to or higher than 1 µm please consider our Maskless Aligner tools.

For more information and specific workflows on either tool, please refer to their respective pages; JEOL JBX-9500FSZ or Raith eLINE Plus.

Getting started and training in E-Beam Lithography

The JEOL 9500 system has a fairly steep learning curve and the information below and corresponding links are fairly comprehensive and describes uses and options that first time users of the JEOL 9500 system should not venture into. Instead, first time users of the JEOL 9500 system should consult our dedicated My First JEOL 9500 Exposure guide which showcases a JEOL 9500 job from start to finish in a tutorial form.

Please request training in E-Beam lithography by sending an email with your process flow to training@nanolab.dtu.dk.

JEOL 9500 and Raith eLine Plus specifications

EBL system comparison table
Equipment		JEOL JBX-9500FSZ	Raith eLINE Plus
Performance	Resolution	8 nm	35 nm
	Maximum writing field	1mm x 1mm	1mm x 1mm
Process parameter range	Acceleration voltage	100 kV	1-30 kV
	Scan speed	100 MHz	20 MHz
	Min. electron beam size	4 nm	10 nm
	Min. step size	0.25 nm	1 nm
	Beam current range	0.1 nA to 100 nA	0.01 to 12 nA
	Minimum dwell time	10 ns	50 ns
Samples	Batch size	Wafer cassettes: 6 x 2" wafers 2 x 4" wafers 1 x 6" wafer 1 x 8" wafer Special chip cassette with slit openings of 20 mm (position A), 12 mm (position B), 8 mm (position C) and 4 mm (position D).	Chips up to 75 x 75 mm 4" wafer holder 6" wafer holder (stage movement limited to central 100 x 100 mm region)
	Substrate material allowed	Silicon, quartz, pyrex, III-V materials Wafers with layers of silicon oxide or silicon (oxy)nitride Wafers with layers of metal	Silicon, quartz, pyrex, III-V materials Wafers with layers of silicon oxide or silicon (oxy)nitride Wafers with layers of metal
General considerations	Pros	100 kV Sub 10 nm resolution Automatic beam optimization High current and process speed Automatic sample exchange High level of programmability for automatic job execution EBL workhorse for large designs	Readily available More intuitive software Easier SEM mode alignment Build in SEM automation for post exposure process control 2D stacks (HBN/graphene) allowed without Al coating Excellent for small chips or small area design exposure
	Cons	Steep learning curve Availability - booking calendar is usually full 5 weeks ahead	Maximum 30 kV User dependent performance/beam optimization Minimum feature size >35 nm Difficult to handle design files >1 GB Slower writing speed

Fundementals of EBL pattern writing

It is important to understand how the pattern is written to understand the limitations of the systems. Let us look at a single piece of geometry to be written; a simple box. Before writing is started the individual shot positions will be assigned to fill in the box at the chosen substrate location. For a simple box the beam shots will sit in a square grid as illustrated below. Pattern writing is a serial process comprised of the following steps

1. Stage movement
2. Beam positioning
   • Unblanking the beam
   • Exposure
   • Blanking the beam

Once writing starts the stage will move the substrate below the column. The beam will be positioned for the first shot and the beam blanker will switch off to start exposure of that shot position. Once the required time has passed (based on current and exposure dose) the beam will be blanked and will be repositioned for the next shot. Steps 2 to 5 will repeat until all geometry in that writing field has been written. At that point the stage will move to the next writing field and the process continues as illustrated below.

Generalized workflow

While the EBL workflow resembles that of UV lithography there are a few additional complications and the parameter space is somewhat larger. The complications all arise from using electrons rather than light for exposure. Since a beam of electrons is used for exposure the substrate must be sufficiently conductive and grounded in order not to build up a charge. If the substrate in itself is not conductive a thin metal film or other conductive surface layer must be applied to it, read more on this in the resist section. Another complication is secondary exposure from backscattered electrons. This is a much bigger topic and covered in the pattern preparation section. A generalised workflow is shown below.

Since substrate preparation and development processes are (nearly) identical for the JEOL and Raith eLine systems they are described in common below. Pattern preparation, job preparation and job execution are fairly different between the two tools and hence these steps are described on the specific tool pages.

Substrate preparation

Substrates must be prepared for EBL bla blah. Read more on the EBL substrate preparation guide

Pattern preparation

Pattern preparation is somewhat different depending on if a pattern is exposed on JEOL 9500 or Raith eLine Plus. Please refer to the correct pattern preparation section below.

Pattern preparation for exposure on JEOL 9500.

Pattern preparation for exposure on Raith eLine Plus.

Job preparation

Job preparation is also different depending on if a pattern is exposed on JEOL 9500 or Raith eLine Plus. Please refer to the correct job preparation section below.

Job preparation for exposure on JEOL 9500.

Job preparation for exposure on Raith eLine Plus.

Job execution

Job execution is covered by the respective tool usage manuals found here

• JEOL 9500 user manual
• Raith eLine Plus user manual

Development

AR 600-546 and ZED N-50 developers are available in a semi automatic puddle developer Developer: E-beam in E-4, mainly intended for development of AR-P 6200 and ZEP 520A. It has automatic recipes for puddle development cycles for 10, 30 and 60 seconds of either of the two developers, each finishing off with an IPA rinse and drying cycle. The system can handle chips, 2", 4" and 6" wafers.

Other resist have to be developed in the E-beam developer fumehood in E-4 in beakers. Please notice there are specific beaker sets for alkaline developers and for solvent based developers.

Post development inspection

After development it is often necesarry to evaluate the result by SEM to verify feature dimensions. This can conviently be done in the Raith eLine Plus tool which apart from being an EBL tool is also a semiautomatic SEM. The strong suit of the tool is the ability to link/align a design file to the substrate and simply define image positions in the design file. The user can then set up a long list of image locations and the tool will acquire the SEM images without further user input. When set up correctly the system can acquire about one image per 5 seconds which is very advantageous for large arrays of structures. For an introduction to this, please refer to our automatic SEM introduction video.

After image acquisition the images can be semi automatically processed with ProSEM to determine feature sizes. For large image sets the software can generate an Excel sheet with various dimension outputs.

Literature on E-beam Lithography

• Handbook of Microlithography, Micromachining, and Microfabrication, Volume 1: Microlithography, P. Rai-Choudhury (Editor), chapter 2 (p 139 – 250). Link to book can be found here: http://www.cnf.cornell.edu/cnf_spietoc.html
• Lithography, Wiley, 2011: Chapter 3, Electron Beam Lithography by Stefan Landis: http://onlinelibrary.wiley.com/doi/10.1002/9781118557662.ch3/summary