The effect of dose rate on ion implanted impurity profiles in single-crystal silicon has been carefully and systematically examined. It "is found that for both boron (light mass) and arsenic (heavy mass), the dose rate has a small but clearly observable effect on channeling tails with higher beam currents producing shallower profiles in the channeling tail. The effect is greater for on-axis (0 ~ tilt/0 ~ rotation) implantation than for off-axis (8 to 9 ~ tilt/30 ~ rotation) implantation, for which there is a clear indication of a dose rate effect for boron, but the effect is negligible for arsenic. Lower mass (boron) implants have a more significant dose rate effect than do higher mass (arsenic) implants. The possible mechanisms that result in this interesting dose rate effect are discussed.
Low-energy arsenic implants used in the formation of ultrashallow junctions are characterized on a high current ion implanter. Significant advantages in beam current and process throughput are demonstrated by using the arsenic dimer ion
(normalAs2+)
for implant energies lower than
5keV
. Dimer implants require only half the dose and use twice the energy of equivalent
normalAs+
implants, resulting in significantly reduced implant times. Process results including Thermawave (TW), sheet resistance
(Rnormals)
, secondary ion mass spectrometry (SIMS) profiles, electrical test and yield show equivalence between
As+
and
As2+
implants.
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