Improved dose performance using Threshold Activated Dose Control™

It is well understood that most high current implant processes are sensitive to dosing variations, and that implanting into photoresist can cause significant dosing related issues due to photoresist out gassing. Methods to control these dosing issues include improving process chamber pumping speed, stabilizing the photoresist mask, reducing ion beam current, splitting the process into steps with an initial lower ion beam current and a subsequent step or steps with increasing ion beam current, and pressure compensation algorithms that utilize a process chamber pressure feedback loop to correct for pressure related charge exchange. In many cases pressure compensation algorithms can effectively deal with pressure related dosing errors without negatively impacting throughput or requiring additional processing steps. Pressure compensation relies on the accurate measure of pressure in the process chamber, which is generally provided by a hot cathode ion gauge. These gauges can become a significant source of dosing variation if allowed to drift over time or if proper calibration procedures are not followed. As the process chamber pressure increases above 1.5 × 10^-4 torr the faraday of some systems produce erroneous readings that cannot be compensated with existing pressure compensation algorithms. This paper shows a non-linear response of pressure vs. beam current at pressures above 1.5 × 10^-4 torr with several level ion beams that is related to photoresist out gassing process chamber pressure increases. This paper also shows the successful implementation of Threshold Activated Dose Control (TADC™), stabilized ion gauges and a proper ion gauge calibration procedures result in an improved dose repeatability and uniformity.