minimize thermal variation across the tube as well as any leakage
at the load door. Results over 14 months showed no significant
variation on any of the tubes or long term drift (see Figures 2– 5).
Additional data for refractive index, film stress, etch rate, and
critical dimensions did not show significant difference except for
the buffered oxide etch rate, which was 0.4% slower for the steamer
grown oxide (see Figures 6–10).
There was a small statistical difference in buffered oxide etch
rate, but only 0.4% ( 20 Angstrom measurement difference), which
was most likely due to a slight difference in film density (growth
rate). BOE (buffered oxide etch ) rate was considerably more sensi-
There was no significant difference in etch rate for reactive ion
etch chamber.
The post-photolithography/reactive ion etch test showed that
results were the same using the pyrolytic method and the steamer
(see Table 1).
Maintenance and Reliability
New technology is often suspect until proven reliable. The MEMS
manufacturer ran our steamer with multiple tools over an extended
period of time to test its reliability. The results were positive. The
steamer had only two component failures over 3 systems within 16
months. These included one infra-red lamp and one steam purifier
assembly. The lamp is considered a service item with a recommended six month replacement cycle. Steamers have a redundant
Steamer
8/14/2007 3:17AM
(First Production Lot)
Pyrolytic
8/13/2007
through 8/14/2007
Table 1. Chart of post-photolithography/reactive ion etch test
Measurement timeframe
for production lot(s)
Critical Dimension
grand average 3.432 3.432
Standard Deviation average 0.024 0.024
heater to prevent loss of the process lot from a heater failure.
Even though the pyrolytic torch has been used for over twenty
years, process failures continue to occur randomly, averaging one
every six months (see Table 2). Depending on the process, this
requires rerunning the lot or even scrapping the entire lot. Torch
issues involve the torch itself, the safety system—which frequently
generates false alarms—and the gas delivery system, which was
cylinder based in this application.
Cost of ownership analysis shows a quick return on the initial
investment. The gas saving alone gave a six month return on
investment. The steamer improved the bottom line in three critical
cost areas:
Consumables: the steamer delivers approximately $12.50/hr or
