Where lithographic processes require the alignment of structures on only one side of the device wafer (e.g. RDL, microbumping and similar techniques), top-side alignment is used to align the fiducials on the mask with those of the wafer. Depending on substrate properties, this can be achieved either using stored position data for the wafer or through live image alignment, as in the DirectAligntm system invented at SUSS MicroTec.
Multilayer wafer stacks are used in a number of structuring processes. By means of infrared (IR) illumination, the alignment marks that in the typical case are embedded between the layers can be identified and aligned.
Alignment can also be done using IR light based on such embedded marks. These require the use of materials that are transparent for IR light, such as undoped silicon, III-V semiconductors (e.g. GaAs) and adhesives for temporary bonding and debonding techniques. Specific cases should be tested to verify process feasibility.
In order to ensure availability of IR alignment to the greatest possible extent, the SUSS equipment can be optionally equipped with powerful IR light sources and high performance camera systems.
The lower the exposure gap from mask to wafer, the higher the resolution. In soft contact mode the wafer is brought into contact with the mask and is fixed onto the chuck with vacuum.
In hard contact mode the wafer is brought in direct contact with the mask, while positive nitrogen pressure is used to press the substrate against the mask. In hard contact mode a resolution in the 1 micron range is possible.
The large gap optics (LGO) optics is optimized for thick resist processes with large exposure gaps and 3D lithography, offering a resolution down to 5μm. The high resolution optics (HR) is apt for contact and close proximity lithography with structures down to 3μm at 20μm exposure gap. For processes with high dose requirements on 150mm wafers the exceptionally high intensity of the W150 HR optics facilitates high throughput.
The diffraction reducing exposure optics is designed to compensate diffraction effects in both contact and proximity lithography. Instead of using a plane wave as in other proximity lithography tools it provides an angular spectrum of planar light waves to reduce diffraction effects. The selection of a proper angular spectrum improves structure resolution in the resist.
MO Exposure Optics® is a unique illumination optics specifically designed for SUSS mask aligners. It is based on micro-lens plates instead of macroscopic lens assemblies. A simple plug & play changeover allows for a quick and easy changeover between different angular settings including the functionality of both classical SUSS HR and LGO illumination optics.
The telecentric illumination which is provided by the MO Exposure Optics improves light uniformity and leads to a larger process window. In consequence, this causes yield enhancements. MO Exposure Optics also decouples the exposure light from the lamp source thus small misalignments of the lamp do not affect the light uniformity. A decoupled light source saves setup and maintenance time and guarantees uniform illumination conditions during the full life-time of the lamp.
SUSS mask aligners are equipped with a WEC head system that allows reaching the parallelism between substrate and mask with a micrometric precision.
Simulation of lithographic processes
A simulation of lithographic processes makes the selection of optimal settings for process parameters possible without long-winded trial and error sessions. The multi-functional simulation software of lithographic processes “Lab”, which SUSS MicroTec distributes together with the supplier, GenISys, first and foremost allows the operator better process control. It offers all the required simulation functionality for an integrated design and process development, as well as verification and optimization. At the same time it covers all the process steps from illumination shaping and mask layout optimization up to photo resist processing. Additionally, modern 3D simulation functions improve the model visualizations.
The combination of MO Exposure Optics and the for SUSS optics custom-developed optical models in Lab facilitates customer-specific design optimization of the exposure filter plates, which in turn leads to an improvement in pattern fidelity.
Imprint lithography represents a cost-effective and highly reliable means of transferring three-dimensional nano- or micro-scale patterns onto a wide variety of substrates.
For the imprint, a stamp is brought into contact with a photosensitive material on the substrate. The photoresist fills out the three-dimensional pattern of the stamp and then solidifies under UV light. Parameters such as pattern topography, structure resolution and aspect ratio have a considerable influence on the process quality.
Thanks to its compatibility to well-established semiconductor processes, imprint lithography plays a key role in the development and production of DFB lasers, HB LEDs, wafer-level cameras and MEMS.
SUSS MicroTec solutions for imprint lithography are based on manual mask aligner platforms and support a wide range of materials and substrate with sizes up to 200 mm. Furthermore, SUSS platforms provide the capability of aligning and levelling stamps to substrates, as required by many imprint applications. Imprint equipment can also be retrofitted to SUSS mask aligners which are already in the field.
Depending on process requirements, SUSS MicroTec offers different imprint technologies on its mask aligners.
Using UV-NIL (UV nano-imprint lithography) SUSS MicroTec offers a classic imprint process to transfer patterns having a resolution down to 50 nm with superior fidelity. The transfer of the patterns is achieved using a hard quartz glass stamp, which is brought into contact with a UV-sensitive photoresist on the substrate. This setup allows very precise control of process parameters such as pressure, process gap and duration. The UV-NIL method allows the highest resolution of the three SUSS MicroTec imprint processes and is recommended for all R&D setups due to ease of use.
|Mask and Wafer / Substrate|
|Wafer Size||1 up to 100 mm / 4" (round)|
|Max. Substrate Size||100 x 100 mm|
|Min. Pieces||5 x 5 mm|
|Wafer Thickness||up to 4 mm|
|Mask Size||standard 2" x 2" up to 5" x 5" (SEMI)|
|Mask Thickness||up to 4.8 mm / 190 mil|
|Contact: soft, hard, vacuum, soft vacuum|
|Vacuum contact adjustable to 200 mbar abs|
|Gap exposure, adjustable gap 10 – 50 µm|
|Flood exposure, split exposure|
|Lamp control modes: constant power, constant intensity|
|Wavelength Range||UV400: 350 – 450 nm (g, h, i-line)
UV 300: 280 – 350 nm
UV 250: 240 – 260 nm
UV 250 / 300 / 400: 240 – 450 nm
|Exposure Source||CPC: Constant Power Controller for lamps
Hg 200 W and Hg 350 W
CIC1200: Constant Intensity Controller for lamps
Hg 200 W, Hg 350 W and HgXE 500 W (Deep UV)
|Uniformity||≤ 3 %|
|Top Side Alignment (TSA) Accuracy||< 0.5 µm (with SUSS recommended wafer targets)|
|Transmitted Infrared Alignment (IR) Accuracy||< 5 µm (2 µm under special process conditions)|
|Alignment Gap||10 – 50 µm|
|MA Movement Range||X: ± 5 mm
Y: ± 5 mm
Theta: ± 5°
|Mechanical Resolution||X, Y: 0.1 µm
Theta: 4 x 10-5°
|Topside Microscope (TSA)|
|Movement Range||X: ± 40 mm
Y: + 30 – 50 mm
Theta: ± 4°
|Vacuum||< – 0.8 bar < 200 hPa abs|
|Compressed Air||5.5 bar (81 psi)|
|Nitrogen||> 1.5 bar (22 psi)|
|Power Voltage||AC 230 V ± 10 %|
|Frequency||50 – 60 Hz|
|Width x Depth||605 x 810 mm = 0.5 m2|
|Weight||up to 130 kg (290 kg with antivibration table)|
|Operator Safety and Ergonomics||CE-mark, others on request
Sound Pressure Level: < 70 db A)
UV radiation emissions (315 – 400 nm): < 0.2 mW/cm