Rapid thermal processing (RTP) generally refers to processes in which semiconductor substrates are heated to high temperatures (e.g., typically 1,000° C.) in a short period of time (e.g., 5 seconds). RTP is typically used in doping/annealing (e.g., dopant activation and wafer damage recovery), rapid thermal oxidation (e.g., gate oxide formation), contact formation (e.g., metal silicide formation), shallow trench isolation reflowing, and/or other stages of semiconductor manufacturing.
Current commercial RTP systems are typically lamp-based or hot wall-based. Lamp-based RTP systems include an array of tungsten-halogen lamps to heat a substrate predominately via radiation. The hot wall-based RTP systems typically include a resistive heating array, and the heating mechanism is also predominately radiation at high temperature ranges (e.g., greater than about 800° C.). Such radiation-based techniques have low energy transfer efficiencies because, among other things, the heat transfer is emissivity-dependent (e.g., dependent on substrate temperature, substrate material, surface conditions, etc.). As a result, ramp-up rates for such RTP systems are relatively low because a substrate may not efficiently absorb the supplied radiation energy. Accordingly, lamp-based or hot wall-based RTP systems may be inadequate for forming junctions with a small junction depth (e.g., 20-35 nm) and an adequate sheet resistance for source/drain extension as feature dimensions of ULSI devices decrease to around 0.1 μm.
In the last decade, flash lamp-based and pulsed laser-based RTP techniques have been under development. These techniques use pulses of high optical energy to either selectively raise a surface temperature or briefly melt the surface of a semiconductor substrate. Upon termination of an optical pulse, the surface of the substrate rapidly cools via thermal diffusion into the bulk of the substrate material. These techniques, however, are still radiation-based. Thus, the energy transfer efficiency is still low. Also, these techniques involve rapidly quenching the semiconductor substrate after each optical pulse, which can lead to lattice defects and dopant metastability issues. Consequently, junction leakage and dopant redistribution during subsequent thermal processing stages may result. Accordingly, several improvements to the current RTP systems and techniques may be desirable.