Applications of Laser Micromachining in Semiconductor/MEMS Industry

Fabrication and machining of MEMS demand a great deal of quality, reliability and productivity of the utilised machining systems. All systems provide the user with an outstanding laser quality, optimised handling components, as well as profitability. Independent on whether wafers made of silicon (Si), gallium arsenide (GaAs), germanium (Ge), gallium phosphide (GaP), indium phosphide (InP), sapphire, quartz, or pyrex shall be machined, all workstations are fitted to the corresponding customer’s application and comply with the established industry standards (SEMI, etc.). Even for smaller lots, features of a larger system can be attained by suitable stages of extension.

Blind holes as well as clearance holes can be obtained. A particularly large development potential is attached to the usage of novel helical drilling heads for the generation of micro holes (diameter > 50 µm) with precisely controllable taper in up to 2 mm thick metal sheets. With the advent of the latter technology, entirely new perspectives for design and functionalisation of MEMS are opened.

In the realm of MEMS, foils, semiconductors, or ceramics can be machined on the 10 µm scale using laser fine blanking, microstructures possessing a resolution of less than 10 µm can be cut and 3D objects can be generated. Capabilities are to be found in the cutting of plastics masks or metal stencils. For the machining of metals and ceramics, solid-state lasers are suited best, while plastics and glasses are commonly machined with Excimer or CO2 lasers.

Lasers are, based on the outstanding ability to finely focus them, capable of extremely precisely and even selectively ablate materials from metals, ceramics, polymers or multilayer stacks. Machining in this range is preferably done with short-pulsed or ultrashort pulsed lasers. The latter tools allow for the generation of smallest possible microstructures (< 15 µm), the fabrication of 3D objects, and layer-by-layer ablation of coatings. These technologies are utilised upon removal of plastic coatings on printed circuit boards (PCB’s), upon the ablation of photoresist layers or upon 2d or 3d structuring of ITO/TCO on PCB’s or piezoceramics.

Laser Micro Engraving

Using laser, all materials established in semiconductor industry, including semiconducting materials, metals, glasses, polymers, or ceramics, can be labelled. The marking of wafers and PCB’s act as a means for tracking and tracing the fabrication process. The marking ought to be machine-readable, should not exert any influence on other fabrication steps and should, even at the end of the manufacturing process, enable doubtless identification. Therefore, highest attainable precision of the laser workstation is mandatory. Moreover, facilities need to comply with requirements made by highest clean-room classifications.

Advantages over conventional processes include:

• Minimised marking size
• High process reliability and machining speed
• Low running costs
• Fraud resistant and indelible labelling
• Marking free of corrosion and bulging
• Prevention of micro cracks

Using Nd:YAG lasers, wafers are, close to their rim, normally labelled with plain text, bar codes, dot-matix codes, or a combination of the aforementioned. For PCB engraving, dependent on special customers demands, also Nd:YAG-, excimer- or CO2 lasers are used. All 3D-Micromac systems are available as stand-alone workstations or as inline-intergration units for easy implementation into existing production lines.

Marking of Wafers

Dependent on process and marking depth, a subdivision into hard marking and soft marking is commonly made. Hard marking ensures a durable marking of the wafer even after numerous etching and polishing steps. Engraved dots possess diameters of between 70 and 110 µm and a depth of up to 100 µm, they are generated by materials ablation. On the contrary, soft marking is based on superficial melting of the substrate and reaches a depth of about 2.5 µm at typical dot diameters of 50 to 80 µm. Softmarking is suitable for cleanroom environments since no particles are generated.