Microelectromechanical methods (MEMS) are miniaturized methods that may be difficult to make and are comparatively fragile. MEMS are sometimes smaller than 1 millimeter and are constructed into elements discovered within the electronics, automotive, medical and communications industries.
“As the identify implies, MEMS includes the interplay {of electrical} and mechanical movement on the micro degree. MEMS gadgets usually include a free-moving mechanical half, corresponding to a cantilever or diaphragm, whose movement is attributable to {an electrical} enter or whose mechanical movement causes {an electrical} output.
David Springer, analysis and growth and product supervisor, KLA
As a part of the MEMS manufacturing course of, getting these small elements transferring is important. To do that, these microstructures have to be quickly supported by a “sacrificial layer”, often made from silicon oxide or silicon. Once the construction of the machine is full, the sacrificial layer is eliminated in order that the MEMS microstructure may be “released” and moved as wanted.
Silicon MEMS Release With HF Vapor
Sacrificial silicon oxide layers are often eliminated by hydrogen fluoride (HF) etching, the place liquid HF reacts with silicon oxide to type the fuel silicon tetrafluoride (SiF4), plus water.
However, if this combination or subsequent rinse options dry, it could possibly trigger “stiffness” by contracting the fragile, free-moving microstructures. These “stuck” constructions stick collectively completely after launch, decreasing the yield of the machine. Another potential downside with moist HF etching is that the excessive focus of water can corrode uncovered metals, particularly aluminum, which is often used on MEMS wafers.
Dry HF vapor can be utilized to keep away from these issues. A gaseous etchant penetrates smaller options extra simply than a moist etchant, permitting for smaller machine designs with longer undercuts.
Primaxx from KLA® The VHF etch launch course of makes use of 100% anhydrous HF and ethanol for the dry HF vapor resolution.
The ethanol ionizes the HF vapor and acts as a catalyst retaining all the things in a gaseous state.
Water, a by-product of the response, additionally acts as a catalyst and is rigorously managed. KLA’s Primaxx course of, which makes use of lowered stress and elevated temperature, removes water from the system. This course of is obtainable on a number of HF etching methods starting from the Primaxx uEtch for analysis and growth to Primaxx Monarch collection platforms for batch processing wafers from 150mm to 300mm in large-scale manufacturing. More than 200 Primaxx modules are utilized by researchers and plenty of producers of high-volume MEMS gadgets.
Learn extra about KLA’s HF Vapor Etch options right here.
Xenon Difluoride For Releasing Non-silicon MEMS
As MEMS turn out to be extra advanced, they might include elements made from a number of or non-standard supplies. Devices may be made with any mixture of silicon dioxide, silicon nitride, polymers, plus most metals and dielectrics. In these instances, the sacrificial layer could also be silicon. Xenon difluoride (XeF2) can be utilized to isotopically etch silicon (Si), molybdenum (Mo), and germanium (Ge), and no different isotropic etch is as selective for these three supplies as it’s for many different supplies.
Importantly, XeF2 Will not assault most supplies generally utilized in packaging or wafer slicing. As a consequence, XeF2 can enhance yield by delaying the discharge of a MEMS machine till dicing is full or the bundle is inserted and the wire is related. XeF2 has been efficiently used to launch MEMS gadgets onto diced wafers on the slicing body and chips in packages and presents very related advantages to utilizing HF vapor to etch silicon oxide. Click right here to be taught extra about KLA’s XeF2 options.
Advantages Of Dry Launch Etching Processes
Using the dry course of eliminates stitching to optimize machine yield with out corrosion of aluminum bond pads. It additionally presents secure efficiency with a large course of window.
Application Examples
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Source: www.kla.com