why does turbo pump throttle gate valve control pressure for deposition

A TURBO PUMP (turbomolecular pump) pulls the chamber down to high vacuum — it's what achieves the clean, low-pressure environment needed for good film quality. The THROTTLE GATE VALVE is a variable valve between the chamber and the pump that controls the PRESSURE during processing — you can run the pump at full speed while the valve opens/closes to hold the exact process pressure. WHY PRESSURE MATTERS: repeatable deposition needs repeatable pressure — pressure changes gas density and reaction rates, so it changes the film. The key line: 'The turbo gets you to clean high vacuum, and the throttle valve holds the exact process pressure — and repeatable pressure is what makes repeatable films.' Your round-2 history covered Turbo Pump and Throttle Gate Valve — know the WHY (pressure control = film repeatability), not just the names.