The SUSS DSM offers front-to-back side measurements for a broad range of applications and substrates. Results specify shift, rotation and run-out components of the offset vector. The system requires a remarkably small footprint and by that low cost of ownership. At the same time, it provides reliable and extremely accurate metrology for double-sided alignment and exposure applications, which are frequently used in the manufacturing of MEMS devices, power semiconductors and optoelectronics.
≤ 0.2 µm measurement accuracy
Double-side or single-side alignment measurement
Optional IR illumination
High throughput and small footprint deliver low cost of ownership
Customized substrate handling solutions available
Accurate metrology for double-sided substrates
SUSS MicroTec has more than 40 years of experience in double-side lithography processes. The processing of double-sided substrates requires an accurate measurement to verify front-to-back side alignment. The DSM8 Gen2 metrology equipment is a recipe-based system and automatically measures and calibrates itself, with manual substrate loading and unloading. This ensures high performance independent of operator’s skills. The fully automated DSM200 Gen2 also features a robotic substrate handling system with customized handling options available, including unique measurement chucks. Optional IR illumination function enables through-silicon measurement capability.
Precise Dual Microscope Metrology
Using a single microscope and looking through a substrate suffers the systematic offsets due to light diffraction and mechanical tolerances. SUSS DSM eliminates this by using double microscope technology to look at alignment features directly and without movement. This system also incorporates Cognex PatMax® image analysis software that delivers optimum precision with industry-proven stability.
Accuracy via TIS Compensation
Eliminating mechanical tool induced shift (TIS) is required for optimum measurement accuracy. The SUSS DSM achieves this by comparing the measurement result of the substrate at 0° with the result at 180°. Image registration of the rotated target images, and accurate offset calculation is performed with the capabilities of Cognex PatMax®.
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.
Alignment of the structuring on the wafer back side with the structures on the front is required in processes involving applications such as MEMS, wafer-level packaging and 3D integration, where used for example to create vertical through silicon vias (TSVs) on interposers. Optical bottom side alignment is normally used for this type of alignment. An integrated camera system detects the mask structures and the structures on the wafer back side and aligns them with each other. The wafer position has to be determined and stored prior to loading, since the wafer afterwards conceals the mask target. This places specialized demands on the alignment system as a whole.
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 DSM 200 is designed for integration into a fab automation system compatible to the SECS-II/GEM interface standards. Level and details of the communication will be specified on basis of the SUSS MicroTec core software solution.
Handling Fragile and Bent Substrates
Handling wafers is the major challenge when automating production processes. In a production environment with high process change rates and therefore a large number of different substrates, for example in foundry production, the handling systems have to meet rapidly changing requirements. The reliability of the automatic handling has a direct effect on through-put and yield. SUSS equipment has a choice of flexibly interchangeable special tooling for handling the widest range of fragile or bent substrates, and the tooling can be customized even further for particularly arduous production processes according to customer specifications.
Handling of Thinned Wafers
A special vacuum chuck supports ultra-thin wafers with thicknesses of less than 120 µm and down to 50 µm.
A special carrier system protects the wafer, especially suitable for the protection of double-sided structures as for MEMS applications.