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Technology Stocks : Align-Rite Int'l (MASK) Undervalued compared to PLAB DPMI
PLAB 21.71-4.3%Nov 7 9:30 AM EST
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To: Christopher Brainard who wrote ()10/12/1997 7:01:00 PM
From: Doug Rife   of 388
 
PLAB's higher valuation reflects its market leadership, second only to Dupont, as well as its electron-beam mask-making technology which is a virtual requirement for producing the next generation of 0.25 micron line-wide chips.

Because photomasks cannot be perfectly aligned with patterns on a silicon wafer made by previous exposures through other photomasks, the line-width or resolution requirement of the photomasks themselves must be of a higher order, that is much smaller than 0.25 micron. Such high resolution is not possible with visible light and barely possible in the deep ultrviolet but the wavelength of electron beams, per quantum mechanics theory, can be made arbitraily small at a high enough beam energy thus easily achieving sub 0.25 micron resolution.

The only reason electron-beam lithography is not used to expose silicon wafers directly is the long exposure times required since you have to scan the beam over the whole wafer surface. Light exposure of the wafer thorugh a photomask is much faster. But since one photomask can be used to expose many thousands of wafers it IS cost effective to use electron-beam lithography to make the photomasks themselves.

There is a facinating article about these issues in the October issue of Physics Today titled "Reading and Writing with Electron Beams" by J. Murray Gibson. I'm not sure if there is an online version although Physics Today is published by the American Institute of Physics at aip.org. WARNING: Not for the casual reader.

There is another article in the same issue titled "On Some Modern Uses of the Electron in Logic and Memory" by Alan Fowler of IBM. This article should be read by anyone interested in understanding the ultimate theoretical speed and density limits of silicon devices. This article also makes me question chip companies based on GaAs technology since it shows why silicon can compete with GaAs on speed based on the smaller line-widths possible in silicon. In essense, the inherent speed (electron mobility) of GaAs is much higher than silicon but is of little practical use if GaAs line-widths cannot be made as small as those achievable in silicon since device speed depends not only on the material but equally on the size of the transistors -- the smaller the faster. Some bearish implications for VTSS?

When the transition to 0.25 micron silicon devices arrives, and it will certainly arrive, PLAB will be in the best position to provide photomasks of the required resolution.
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