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Diamond Scribers Hold The Aces

Last month, we looked at laser scribing for back-end wafer processing. Here, we ask James Loomis of Loomis Industries about the technological advantages of diamond scribe dicing.
Compound Semiconductor: When did the industry first use diamond scribers?


James Loomis: During the 1960s and early 1970s all semiconductor wafers were scribe-diced, but yields were erratic because the tools were not manufactured or held in the machine properly. I invented a superior scribing process, and since 1972 Loomis Industries has worked with its customers to develop and perfect diamond scribe dicing procedures that give industry standard yields of over 99% for virtually all compound semiconductor devices other than GaN (see table 1). Our tools have been applied to GaAs FETs, LEDs and other III-V devices since 1979, and we have customers who have used the same machine on a 24 h/7 day continuous cycle for 10-15 years.

CS: What are the key advantages of diamond scribe dicing?


JL: Scribe dicing is reliable. With a narrow scribe line and controlled fracture, die street widths can be narrowed to 35 µm (150 mm wafers) and 20 µm (50 mm wafers). Even a modest decrease in street width will increase the number of dice per wafer dramatically. There is no loss from contamination or degradation in die performance. Other processes can degrade device efficiency by up to 15%.

Scribe dicing is clean and safe. No wafer material is removed and no debris or hazardous by-products are created. It is a dry process that doesn t require water or any pre-coating of the wafer to protect the devices, so a subsequent cleaning step is not required.

It is also economical. The initial cost of a Loomis scribe dicing machine is one-third of that of competing equipment, maintenance is non-specialized and routine service requires minimal technical expertise. Downtime is negligible and machine life is 10 years or more. Power consumption is minimal, while consumable scribe tool costs are modest. The compact machines require much less costly cleanroom space with no need for venting.

CS: How is Loomis responding to the threat of new wafer-dicing methods?


JL: While other scribe dicing manufacturers have felt pressure from alternative technologies, Loomis has maintained its position in most III-V markets. This is because not all scribing methods are alike. Our patented scribe tool design and innovative manufacturing processes create scribe alignment and precision that controls scribing and breaking at the crystal and molecular level. Our competitors have been unable to approach this level of precision and in essence have been "cutting with the wrong side of the knife".

There is no compelling reason to switch to other technologies; technologies that are often associated with adverse side effects such as damaging debris generation and associated cleaning and waste-removal costs.

CS: How are you tackling scribe dicing of GaN-based devices?


JL: GaN on sapphire or SiC substrates presents us with a new challenge - that of tool wear. These materials are nearly as hard as diamond. The challenge is being met with a new diamond polishing process, and a new scribe tool holder that efficiently uses the [diamond] point. Tool wear for SiC and sapphire is now only one-third of that of our former tools, and [the process is] much more repeatable. The improvement will enhance our scribing process for all compound semiconductors.


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