Diffusion furnace dopant activation matching through a ramped temperature idle

Significant non-uniform 'time at temperature' or Dt variation is observed across a horizontal furnace load in diffusion batch processes. Non uniform activation of dopants is observed in 800degC, short duration processes with high mobility dopant species. Dt matching across the furnace is obtained by changing the temperature zone set points at furnace idle prior to pushing and processing a full wafer batch. A ramped idle temperature ranging 120degC across the furnace improves activation uniformity. Boron implanted test wafers show an 85% reduction in activation non uniformity across the furnace when using a ramped idle.