TimeDomain CVD, Inc.

APCVD Conclusions

Operational Control

Systems are slow to adjust to temperature changes, and somewhat sensitive to ambient conditions since they are open. Care in tool siting and fab surroundings is important.

Film uniformity

Wafer transport velocity and all gas flows must be very precisely controlled to obtain good uniformity in the direction of wafer travel. (This is relatively easy to do, since operation is continuous, without turn-on transients.)

High molar flows mean short diffusion lengths: careful adjustment of gas metering is thus required to obtain good film uniformity perpendicular to travel.

Wafer edge effects are significant.

Productivity advantages

Continuous operation without loading or pumpdown delays means potentially high throughput. Continuous operation also means gas controls run in steady-state mode with no transients for turn-on and turn-off.

Productivity disadvantages

Actual area of deposition is much narrower than the wafer, so peak deposition rate is very high for a given average rate. In consequence, average rates may be relatively low for a given film quality. Larger wafers give reduced WPH out for a given deposition rate.

Major changes in operating conditions (especially temperature) take several hours to stabilize.

Periodic manual cleaning of injectors and transport paths are required.

APCVD reactors have been widely employed for deposition of boron and phosphorus doped silicon dioxide (BPSG), commonly used in the initial dielectric layer after MOS transistors have been formed.

Reactors: Table of Contents

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Operational Control	Systems are slow to adjust to temperature changes, and somewhat sensitive to ambient conditions since they are open. Care in tool siting and fab surroundings is important.

Film uniformity	Wafer transport velocity and all gas flows must be very precisely controlled to obtain good uniformity in the direction of wafer travel. (This is relatively easy to do, since operation is continuous, without turn-on transients.) High molar flows mean short diffusion lengths: careful adjustment of gas metering is thus required to obtain good film uniformity perpendicular to travel. Wafer edge effects are significant.

Productivity advantages	Continuous operation without loading or pumpdown delays means potentially high throughput. Continuous operation also means gas controls run in steady-state mode with no transients for turn-on and turn-off.

Productivity disadvantages	Actual area of deposition is much narrower than the wafer, so peak deposition rate is very high for a given average rate. In consequence, average rates may be relatively low for a given film quality. Larger wafers give reduced WPH out for a given deposition rate. Major changes in operating conditions (especially temperature) take several hours to stabilize. Periodic manual cleaning of injectors and transport paths are required.