Wafer temperature measurement in a rapid thermal processor with modulated lamp power

Pyrometry methods utilizing modulated lamp power ("ripple"! were used to im prove wafer temperature measurement and control in rapid thermal processing (RTP) for silicon integrated circuit production. Data from a manufacturing line where ripple pyrometers have been tested show significantly reduced w afer to wafer and lot to lot variations in final test electrical measuremen ts and increased yields of good chips per wafer. The pyrometers, an outgrow th of Accufiber's ripple technique, are used to compensate for ordinary pro duction variations in the emissivities of the backsides of wafers, which fa ce the pyrometers. Power to the heating lamps is modulated with oscillatory functions of time at either the power line frequency or under software con trol. Fluctuating and quasi-steady components in detected radiation are ana lyzed to suppress background reflections from the lamps and to correct for effective wafer emissivity. Sheet resistances of annealed wafers with high dose shallow As implants were used to infer temperature measurement capabil ity over a range in backside emissivity. Emissivities are varied when depos iting or growing one or more layers of silicon dioxide, silicon nitride, or polycrystalline silicon on the backsides of the wafers.