Editor's Page

Extreme silicon

My recent tour of MEMC Electronic Materials' St. Peters, MO, facility revealed a central truth about silicon wafer manufacturing: It is a business of extremes. Profitability comes under extreme pressure when large amounts of money must be spent on technological innovation in the drive to 300 mm, without much initial return on investment. For example, fourth-quarter results showed a 28% increase in sales compared to the same quarter in 1996, yet the company still incurred losses for the period, largely because of a 48% increase in technology expenses.

There are extremes of heat and cold, with a nearly 3000°C swing from the beyond-icy temperature needed to grow or freeze crystal to the thermal blast necessary to melt polysilicon. Proportions range from 1-Å surface roughness for a finished wafer to 200 kilometers of wire found inside a giant sawing machine that slices wafers from the massive bologna-like "rod" of cooled-down silicon. Cleanliness requirements vary from the tidy industrial machine shops to the better-than-Class-1 cleanrooms where final polishing and analysis occurs. The employee roster includes blue-collar tool operators as well as PhDs on the wafer's edge of advanced technology. The factory's manufacturing cells feature mature toolsets still churning out 4-, 5-, and 6-inch wafers along with first-of-their-kind 300-mm models.

These business extremes are sometimes rich in irony. A few steps after massive crystal pullers transform the raw material and huge sawing tools slice the rods into wafers, much of the wafer's incredible flatness and purity are accomplished through the use of rough abrasives and caustic chemicals. The delicate end-product must be handled with extreme care, lest it be scratched, cracked, dimpled, or broken. Despite this, there are horror stories of clueless truckers who wield crates filled with carefully packaged wafers in a manner befitting boxes of ball bearings or bricks. Once the wafers arrive at their destination, their life span is relatively short: at the end of the device-making process, the remaining silicon is mostly back-ground into oblivion to free the microchip from its bonds. Many influential players in the semiconductor industry are pushing to make wafers a commodity. It's a bit troubling to think that such specialized knowledge and expertise could result in an operation seen as little more than a high-tech version of sliced bread.

Outside those in the wafer business and their customers, few realize the implications of these extremes, taking for granted that the silicon works as it should. Somehow, despite the thin margins and substantial technological and manufacturing challenges, wafer suppliers consistently deliver a high-quality product. The key to this is the starting material. "Crystal is the core reason why you do silicon better than your competitors," explained Dave Sloat, the company's 300-mm commercial manager. It boils down to "how well you do something that everyone else does." MEMC's pilot line for the larger-size wafers began production in March of last year, with "a continuous flow of new equipment" ever since, said Steve Brunkhorst, director of the 300-mm program. His comment that "we build facilities with capacity in mind" resonated throughout the Missouri plant, with construction either under way or recently completed in a number of areas.

The yield issue, both for MEMC's own products and those of its customers, looms large. It is critically important "how well silicon will operate yieldwise in the device line," said Brunkhorst. Productivity and manufacturing efficiency are crucial. The company must "design a process with the fewest steps, the most efficient steps, use resources cost effectively, and end up with a good finished product. . .a wafer with a chemically perfect surface." Achieving high yields ultimately comes down to MEMC's trump card -- its extremely capable workforce.

Tom Cheyney
Editor

tom.cheyney@cancom.com

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