Metal Lift-Off Process
Inexpensively patterning metal for the fabrication of micro-devices such as MEMs, sensors, LEDs, and photonics (to name a few) is a nearly universal, but fundamental process. A common and effective method is to deposit a blanket layer of metal over a patterned release layer such as photoresist. By relying on the adhesion of the metal to the substrate, the dissolution of the underlying resist releases the unwanted metal leaving islands of patterned metal behind. Visually, this process appears to show the layer of metal lifting-off of the substrate which has resulted in the name of Metal Lift-Off (MLO). The combination of a single lithography step and low-cost deposition techniques such as evaporation result in a cost-effective and reliable method of forming a patterned metal layer when dimensions tend toward the larger, and tolerances toward the non-critical.
As with most technologies, there has been an evolution towards smaller features, tighter critical dimensions (CD), and more demanding thickness uniformity. This has resulted in the growing adoption of more rigorous (and slightly more costly) processes based upon patterned plating. Here, metal is electroplated onto the substrate through the open areas of a resist mask onto an underlying barrier and seed layer, followed by a photoresist strip and barrier/seed layer etch (generically referred to as an under-bump metallization etch, or UBM). While the cost of the electroplating step is typically much less than the cost of an equivalent vacuum-based process such as evaporation or sputtering, the additional processing steps add up. In the end, there are still many applications for which metal lift off is a viable, and preferred approach – particularly when smaller substrates such as 100mm, 125mm, 150mm, and 200mm wafers are considered.
For over 30 years, Semitool spray solvent tools, or Semitool SST, have traditionally been the favored equipment for performing the metal lift-off step. Smaller and less costly to operate than wet benches, Spray Solvent Tools, or SSTs, setup for Metal Lift-Off, have the ability to constantly refresh the wafer with a stream of fresh solvent quickly and effectively undercutting unwanted metal.
ClassOne Technology’s Trident™ SST tools breathe new life into these industry workhorses. With a smaller footprint, simple and robust design, and the ability to deliver chemical from up to eight on-board tanks, the Trident packs the horsepower needed to perform demanding metal lift-off processes at fraction of competitor’s batch tools or single-wafer tools such as the SSEC 3xxx platform. Packed with standard features and controlled by the power Windows 7-based Solaris™ controller, Trident sets a new standard for performance and price for your Metal Lift-Off process.
Metal Lift-Off Process: Trident Spray Solvent Tool (SST)