Vacuum Pump System for CVD Chamber Gas Purification
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Solution Overview
Problem
In CVD processes, high growth rates lead to deposition of foreign substances like ammonium chloride on chamber walls and vacuum pump components, causing operational issues due to variable pressure conditions and the need for frequent cleaning or high energy consumption to maintain adequate volume flow rates, which burdens waste-gas treatment systems.
Innovation Solution
A device comprising a dry-compression vacuum pump connected to a liquid ring vacuum pump via an intermediate line, where the pressure is maintained below atmospheric pressure to prevent condensation, allowing foreign substances to be absorbed by the liquid ring pump's operating liquid, and a scavenging gas is used to enhance volume flow rate, with a system for monitoring and replacing the operating liquid to maintain effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If cooling traps are installed downstream of the process chamber to accumulate condensable substances, then deposits can be concentrated at one location, but the cooling traps require frequent cleaning and evacuation which reduces productivity
Solution Approach 1:
The invention extracts the harmful condensation problem from the high-vacuum chamber environment by introducing a second-stage pump (liquid ring vacuum pump) that operates at higher pressure. This separates the condensation issue from the primary vacuum system, allowing continuous operation without interrupting the CVD process for cleaning.
Solution Approach 2:
The patent introduces an intermediate pressure stage between the high-vacuum chamber and atmospheric pressure. The liquid ring vacuum pump acts as an intermediary device that handles the pressure transition, absorbing condensable substances in its operating liquid rather than allowing them to deposit in the vacuum chamber or downstream components.
2Object-affected harmful factors
If intensive heating of lines is applied to maintain adequate volume flow rate, then deposits can be prevented, but energy consumption increases and thermal loading burdens waste-gas treatment
Solution Approach 1:
The invention changes the pressure parameter in the intermediate line to a range (10-100 mbar) where condensation is suppressed without requiring intensive heating. This parameter optimization prevents deposits while minimizing energy consumption compared to thermal solutions.
Solution Approach 2:
The patent uses the liquid ring vacuum pump's hydraulic principle, where the operating liquid creates a seal and transfers energy to maintain gas flow. This pneumatic-hydraulic approach maintains adequate volume flow rate without thermal input, avoiding the energy consumption and thermal loading problems of heating-based solutions.
3Stability of the object's composition
If multiple sealing gaps are introduced in series to keep inlet pressure constant, then pressure stability is improved, but device complexity increases
Solution Approach 1:
The patent segments the vacuum system into two distinct pressure stages: a high-vacuum stage (first-stage pump) and an intermediate-pressure stage (liquid ring vacuum pump). This segmentation isolates the inlet of the first-stage pump from pressure fluctuations at the outlet, maintaining stable operating conditions without requiring multiple sealing gaps within a single pump.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively prevents unwanted deposits by maintaining low pressure and high volume flow rates, reducing the need for additional waste-gas scrubbers and minimizing energy consumption, while ensuring reliable purification of extracted gases.
Implementation Method 1
the pressure and the volume flow rate of the gas which is conducted onward to the liquid ring vacuum pump are set such that condensation of the foreign substances does not yet take place
Implementation Method 2
the foreign substances condense for the first time in the liquid ring vacuum pump and are absorbed by the operating liquid in the latter
Data Source
AI summary
A device evacuates a chamber and purifies the gas extracted from said chamber of any foreign substances. The device comprises a dry-condensing vacuum pump having an input connected to the chamber to be evacuated and is suitable for maintaining the input pressure at a constant level at the output despite variable conditions. An intermediate line which connects to the output of the dry-condensing vacuum pump and a liquid ring vacuum pump, the input of which is connected to the intermediate line, are additionally provided. A corresponding method makes it possible to purify the gas of any foreign substances reliably and effectively.