P. Malone et al., STUDIES OF WAFER SURFACE CHARGING USING THE THOR MONITOR DEVICE, Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms, 96(1-2), 1995, pp. 52-55
The THOR monitor is a Texas Instruments in-house gate oxide integrity
test device used to qualify the charging performance of production imp
lant processes. It has five charge collection antenna on capacitor str
uctures with antenna to gate ratios ranging from 100:1 to 7500:1. The
gate oxide thickness of 200 Angstrom could be considered to be large,
but the addition of photoresist makes this device extremely sensitive
to charging damage. A sensitive THOR photoresist configuration has bee
n studied in conjunction with advanced beam diagnostics in a situation
in which intermittent yield was achieved. A P/150 keV/20 mA implant w
as found to give full yield on the test structure for only approximate
ly half of the implants before enhancements to the flood system overca
me this. Traditional beam diagnostics, such as wheel current, capaciti
ve charge sensor voltage and beam profile width could not predict when
yield would be good or bad. However, measurement of slow ion spectra
before an implant using a cylindrical mirror analyser ion spectrometer
gave good correlation between the slow ion spectrum and THOR yield. T
he variation in slow ion spectrum could be related to ion source tunin
g and demonstrates that although present charge neutralization devices
are sufficient for todays requirements, future charging performance i
mprovements may well come about from understanding the generation of h
igh quality beams and the use of advanced beam diagnostics to aid in a
utomatic implanter tuning.