Showerhead Reactors: Conclusions

Temperature control: Good heat transfer to the wafer by conduction and radiation, but heat losses can be primarily through radiation, and not uniform across wafer. Zone heating is required for good uniformity. Radial temperature changes may be implemented though control is complex.

Radial film uniformity: Adjustable by changes in temperature and showerhead design.

Flexibility: Configuration lends itself to capacitive discharge plasmas for PECVD and chamber cleaning.

Productivity advantages: Batch configuration can be used for small substrates, often with manual loading. Single-wafer configuration with fully automated loading is relatively easy; the reactor is small and easily clustered with other functions. Easy in situ clean with plasma. Every wafer sees an identical environment.

Productivity disadvantages: Single-wafer configuration or mini-batch [e.g. several showerheads in a single chamber] both require high deposition rates for good throughput, which tends to degrade film quality. If the lower platen (wafer chuck) is heated and the ceiling is cold, wafers tend to "potato chip" if loaded without preheat, and can slide on the platen.

Process advantages: Rapid changes in gas conditions for multiple-layer films are possible.

Process disadvantages: Plasma discharges tend to sputter contamination from reactor walls onto wafers, an effect enhanced at electrode edges. The small showerhead dispense holes can clog or erode, degrading uniformity.

Showerhead reactors are widely used for "back end" processes: deposition of intermetal dielectric layers, metals (e.g. CVD tungsten), and final passivation. Small manually-loaded showerhead reactors are very popular in R&D environments due to their versatility.

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