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Introduction

Direct laser lithography or direct laser writing using two-photon deep ultraviolet laser for additive 3d manufacturing using conventional resin sensitive to two-photon absorption resulting in two-photon polymerization to create volumetric prints from CAD models.

Exposure System

The NanoScribe GT2 Laser Lithography System is an ultramodern two-photon polymerization volumetric maskless printer. It is one of our newest acquisitions here at the Cornell NanoScale Facility (CNF). The tool was purchased in late 2019 and delivered and installed during the second week of January 2020. This was accomplished with the help of a committee of faculty and researchers, and a grant from the NSF. The NanoScribe GT2 can create three-dimensional nanostructures using a NIR femtosecond laser via direct-write onto a photosensitive resin, which is subjected to a non-linear two-photon absorption process. This process involves cross-linking the resin via UV absorption. The laser sets a focal light cone where a concentration of the light intensity defines the exposure focal spot volume or a “3D Pixel.” Using this technique, a CAD design can be broken into an X-Y-Z coordinate system to define the structure pixel by pixel and layer by layer. The exposure side of the system sits in a fine-tuned vibration isolation table and a high-speed ultra-precise piezoelectric stage for movement in X-Y-Z and uses a galvanic mirror defection system for focusing and beam rasterization. Models for printing can be designed using the stand-alone software DeScribe—which comes with the tool—or with any CAD software capable of outputting file formats DXF or STL. The DeScribe software can import these formats.

3D Print Technology & Direct wright

Laser-based direct writing has been around for a few years especially in the semiconductor industry know as maskless lithography (MPL). Typically the two-dimensional CAD design is transferred onto the substrate that is pre-coated with a photosensitive resin via reduction laser projection. The projected pattern was reduced given the tool's numerical aperture and scan across the surface of the substrate using either a raster or vector format. These techniques are the same ones utilized in 3D direct-write. The only difference is that know you are working with a thickness degree of freedom that can be scanned across the Z-axis. The NanoScribe GT2 has a Piezo Nanopositioning stage and a high-speed galvo scanner. In the case of two-photon lithography, the light source is a pulsed femtosecond fiber laser with the center wavelength being around 780 nm.

Hardware Overview

Diagram of a simplified optical path of a Two-Photon Lithography System.

Two-photon Light Source

  • Hight Performance NIR femtosecond laser 

Tool Training

Cornell NanoScale's Training Workflow

  • Send the tool manager a request for online access to NanoScribe’s NanoGuide Web-page.
  • Users are required and responsible for reviewing the services and procedures provided by NanoScribe on the following: [You will need to log in to NanoGuide to view these materials.]
  • Import a CAD model File
  • Prepare a sample & change the objective
    • The end-user is responsible for maintaining their own supply of substrates.
    • CNF will provide at no extra charge standard resist. 
    • Standard resins are:
      • IP-Dip
      • IP-S
      • IP-L
      • IP-Q
  • Start NanoWrite and Insert sample holder

      • Perform a sample approach

      • Load a print Job

      • Print your structure

      • Unload the sample

      • Develop the sample

      • Clean the objective lens

      • Leaving the printer

      • 3D Printer

        • Overview and Safety
        • Software (Software Overview, DeScribe, NanoWrite, Zeiss Axion Vision)
        • Sample Holders
        • Print Sets
        • Hardware
        • Objectives (Objective Overview, 63x, 25x, 10x)
        • Substrates
        • Cleaning and Maintenace
      • Process Materials
      • Printing Processes
        • Model Creation and Import
        • Print with Solution Sets
        • Print Strategies
        • Programming Structures
        • Post Print Processes
      • (Optional) Learning
  • (For additional remote and e-learning from NanoScribe)
    Check your STL model for common mesh errors. You can use a cad software capable of mesh verification such as Autodesk Meshmixer or MeshLab
  •  Once your file has been checked for mesh errors, run it through DeScribe to do the conversion. Be sure to select the desired solution set (SF, MF, or LF) for your process. 
  • Sign up in CULearn for training:
  • Once you have watched the online CULearn training video send the tool manager to arrange hands-on training. 

NanoScribe's Subsystems

  • Electronics Cabinet

  • Optics Cabinet [contains the laser, optics, and Galvo]

  • Emergency Off (EMO) switch

  • Printing Cabinet [Microscope, Piezo, and Stage]

  • Power Supply 232

  • System Controller

  • System Computer

  • Laser System Controller

  • Galvo Stage Power Supply

  • Monitor, Keyboard, and Mouse

  • Manual Microscope Controller

  • Joystick

Power UP and Power DOWN Procedures

Power UP Procedure

Warning!

"Disregard of the guidelines concerning power-up of the Photonic Professional GT2 may cause damage to the system!"

Apply the following sequence in order to power up the Photonic Professional GT2 (See Fig)

  1. Turn the mains power switch to position 1.

  2. Wait some seconds until the reset and open buttons blink in alternation and the attention indicator is lit up.

  3. Press the reset button, the attention indicator switches off.

  4. Switch on the Photonic Professional GT2 Controller by activating the key switch.

  5. Switch on the Control PC: Let it boot completely before proceeding, wait until the long on-screen shows up.

  6. Switch on the laser controller by activating the key switch. The button start/stop does not have to be pushed (the backlight of the button should be off). The laser emission is controlled via the Photonic Professional GT2 control software NanoWrite.

  7. Switch on the GT power supply.

  8. Switch on the z-drive power supply.

  9. Switch on the computer monitor.

  10. Press the open button in order to release the safety lock and to open the printing cabinet. As long as the safety lock is released the open button is blinking white.

    Note: The laser gives acoustic feedback, as soon as its start-up is finished. This can take up to 30 s. After that, the control software NanoWrite may be launched. Make sure that the laser is operational when starting NanoWrite. The laser emission is switched on automatically when NanoWrite starts. The status of laser emission is indicated by the backlight of the button start/stop on the front panel of the laser controller. If the light is activated, the emission is on. You can manually switch on/off the emission by pressing this button. A power calibration of the laser is performed automatically before the first print starts or when NanoWrite receives the first script command.

Power Down Procedure

Warning!

"Disregard of the guidelines concerning power-up of the Photonic Professional GT2 may cause damage to the system!"

Apply the following sequence in order to shut down the Photonic Professional GT2 (See Fig)

  1. Exit NanoWrite. Wait until NanoWrite is shut down. Otherwise, error messages may occur. In general, the laser emission is switched off automatically when exiting NanoWrite.

  2. Shut down the computer.

  3. Make sure the objective lens is in the lowermost position. Check for the message lower z-limit reached on the touch panel.

  4. Switch off the z-drive power supply.

  5. Switch off the GT power supply.

  6. Check the status of the laser emission; if the backlight of the button start/stop is activated, press it to switch off the emission.

  7. Switch off the laser controller by deactivating the key switch.

  8. Switch off the Photonic Professional GT2 controller by deactivating the key switch.

  9. Switch off the Photonic Professional GT2 by turning the mains power switch to position 0.

Warning!

Never switch off the Photonic Professional GT2 Controller or the mains power switch prior to any of the other components. This might cause damage to the system. The emergency shutdown of the system should only be used under dangerous situations. Do not use it as a standard shut down procedure.

CAD & Software

CAD Model

DeScribe

Alignment & Overlay

Recipes

GWL Programming

Python Scripting

NanoWrite

General Printing

Operational Workflow (SOP) as stated in the NanoGuide

Multi-DiLL Printing

Multiple print Jobs

DiLL Process Substrates used on the tool

  • Fused Silica Substrates
  • Borosilicate Substrate
  • ITO coated Borosilicate Substrates
  • Silicon Substrates


Resins available at the CNF

IP-DIP: IP-Dip is a liquid negative-tone 2PP resin formulation by NanoScribe designed for printing the finest possible features. IP-Dip is a component of the 3D SF Solution Set. Tall structures exceeding the working distance of the objective can be printed using DiLL configuration.

IP-S: IP-S is a highly viscous liquid negative-tone 2PP resin formulation by NanoScribe designed for printing medium-sized features in DiLL. IP-S combines low shrinkage and high stability with a smooth structural surface finish perfect for micro-optics. The photosensitivity is tailored for two-photon polymerization and UV-curing is also possible. As a component of the 3D MF solution set, IP-S is suitable for printing structures with dimensions of several cubic millimeters.

IP-L 780: IP-L 780 is a liquid negative-tone 2PP resin formulation designed for printing small features in oil immersion configuration. IP-L 780 combines high resolution with low shrinkage and high stability.

IP-Q: IP-Q is a highly viscous liquid negative-tone 2PP resin formulation by NanoScribe. The 3D LF Microfabrication Solution Set, including IP-Q, extends 2PP 3D printing towards rapid printing of mesoscale structures with millimeter sizes, micrometer precision and maximum throughput up to the macroscale.

SU-8: SU-8 is a UV-curable negative-tone 2PP resin by Kayaku Advanced Materials. This resin is well-known and widely used in the lithography community. [The following article applies only to SU-8 100 determined to be the most suitable resin for 2PP as it balances quality and printing speed.]

Develop

Metrology & Post Processing

Aspect Ration & Selectivity

Model UV Curing

Model Removal & Resin Stripping


Applications

  • Microfluidics
  • Micromechanics
  • Biomedical Engineering
  • Micro-electro-mechanical systems
  • Mechanical metamaterials
  • Micro-optics
  • Photonic metamaterials and Plasmonics

Publications & Gallery

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