Tutorial #52
George Riley
May 2005/January 2009
Introduction
A new generation of nano-imprint lithography (NIL) production equipment has been developed by S.E.T. Smart Equipment Technology in partnership with VTT Microelectronics, and introduced at Semicon Europa on April 12, 2005. The Nano-imPrinting Stepper NPS300 is the first NIL equipment which offers both hot embossing and UV NIL lithography of wafers in a single step-and-repeat system. The NPS300 provides a sub-20 nm imprinting resolution in a system that is optimized for the cost-effective volume production replication of micro or nanometer scale devices.
By using stamps or templates rather than optical lithography for the imprinting, the NPS300 can replicate patterns under 100 nm. Applications include integrated optical devices such as passive devices on diodes, gratings, photo refractive polymers, back side illumination devices; smart materials for microelectronics, such as sensors, resonators and transducers; sensors for temperature, light, molecules, and biomedical sciences; replication of three-dimensional objects such as MEMs components.
Hot Embossing
Step-and-stamp imprinting for hot embossing is an innovative method that has been previously demonstrated by VTT Microelectronic Center in Finland, using a S.E.T. FC150 Device Bonder. [1] This imprint lithography method consists of transferring the pattern of the stamp into a thermoplastic embossing material by controlling heat and pressure. The pattern may be the final product, or it may be used as a nano-scale mask for further wafer processing.
Figure 1 Sequence for creating a resist mask by step and stamp NIL. (courtesy VTT)
In Step 1, the silicon stamp is positioned over the thermoplastic resist, and heated above the glass transition temperature Tg of the material.
- In Step 2, it is pressed into the resist, softening the material, which flows under pressure to conform to the stamp pattern. Heat and pressure are maintained until the pattern is formed. The stamp is then cooled below Tg to fix the pattern before releasing pressure.
- In Step 3, the stamp is moved to a new position, and the imprinting sequence is repeated.
- In Step 4, the stamp is released and removed.
- In Step 5, a reactive ion etch removes the resist residue from the pattern, forming a resist mask with clear openings.
Figure 2 SEM image of 400 nm wide interdigitated aluminum fingers created by step and stamp NIL followed by an aluminum lift-off process.(courtesy VTT)
UV-NIL Lithography
UV-NIL Lithography( “step and flash”) uses a UV-transparent patterned master template, which is pressed against a UV-curable material to imprint the pattern. The pattern is UV-cured before pressure is released. Cold embossing allows accurate overlay of multiple levels of features, and may be performed on one or both sides of a wafer. Reference [3] give mores details of NIL processing and applications for both hot embossing and cold embossing.
System Capabilities
The NPS300 combination of hot and cold embossing gives the user great flexibility in NIL techniques. The NPS300is available either as a manually loaded machine or as a fully automated system. The automated system includes automated wafer loading and handling for sizes up to 300 mm and an automated template pick up capability, allowing different templates to be printed on same wafer.
When equippedwith the automatic alignment option, the NPS300 has a 250 nm overlay accuracy and accepts stamps with sizes up to 100 mm and with thicknesses up to 6.5 mm. The NPS300 imprinting arm can be equipped with either a cold or a hot embossing head. The imprinting force ranges from 5 newtons to 4,000 newtons. The active area of the stamp can be up to 40 x 40 mm for cold embossing and 100 x 100 mm for hot embossing.
The optical system is a superimposing microscope with high magnification, which combines the images of the stamp with that of the wafer before they reach the video camera. The short working distance allows a high numerical aperture, offering an unsurpassed resolution.
The NPS300 is ideal for performing all of the process steps required for different imprint lithography technologies. This new tool is a cost effective alternative to high resolution e-beam lithography for printing sub-20 nm geometries. In addition to this Nano imPrinting Stepper, S.E.T. also offers full wafer NIL with mask aligners for cold embossing and with substrate bonders for hot embossing of entire wafers in a single step.
References
- “Step and Stamp Imprint Lithography using a Commercial Flip Chip Bonder,” T. Haatainen, Jouni Ahopelto, Gabi Gruetzner, Marion Fink, Karl Pfeiffer, SPIE 25th Annual Symposium of Microlithography, Emerging Lithographic Technologies IV, Santa Clara, CA, USA, 2000.
- “Pattern Transfer using Step & Stamp Imprint Lithography,” T. Haatainen and Jouni Ahopelto, Physica Scripta Vol.67, 357-360, 2003.
- G. A. Riley, “Fabrication of Wafer-Level Nano-Optics,”
Advanced Packaging, November 2004, pp 18 – 25
For more information
S.E.T. www.set-sas.fr
Tutorial 40 ”Nano-Embossing Reaches Production.”
Tutorial 49 ”Fabrication of Wafer-Level Nano-Optics.”