The 1152C Vapor Source Mass Flow Controller is a pressure-based measurement and control system designed to meter and control vapor from low vapor pressure liquid and solid sources directly, without the need of a carrier gas. The 1152C consists of a fixed flow element and two capacitance manometers for flow measurement, with a proportioning solenoid control valve for flow control.
Deliver source vapor without the need of a carrier gas system
Many new processing techniques, such as MOMBE (CBE) for III-V compounds, silicon deposition using TEOS, and plasma polymerization are placing increased demands on mass flow control techniques. All of the above applications use source materials that are liquids or solids at room temperature and require heating to increase the vapor source pressure. Our extensive experience with precision pressure measurement instrumentation made the addition of a pressure measurement-based mass flow meter and controller a natural extension of this technology, and led to the development of the 1150C and 1152C. The 1150/1152 are capable of delivering vaporized liquid source materials such as: TEOS, DADBS, HMDS, TMCTS, TEAL, TEB, TEG, TEI, TMAL, TMB, TMG, TMI, TaCl5 , DMEAA, Ti[OCH(CH3 ) 2 ] 4 , TiCl4 , TIBAL, and TMP.
Viscous Laminar Flow Technology
The 1152C is based on viscous laminar flow technology. The equation describing flow through a laminar tube is Q = K (P12 - P22) where Q is mass flow, K is a constant, P1 is upstream pressure and P2 is downstream pressure. Two capacitance manometers are included so that both upstream and downstream pressures of the flow elements can be monitored. Since the difference and sum of these pressures are required [(P1 -P2 ) x (P1 + P2 )] to compute flow, circuitry for the measurement is also more advanced. The benefit of this approach is the upstream pressures need only be slightly higher than downstream or process pressures, minimizing heating requirements of the source material and allowing use at higher system pressures.
In application, the 1150/1152 is placed downstream of the source material oven. Precise temperature control is not required as the unit control loop will compensate for inlet pressure variations. Delivery lines to or from the 1150/1152, or from the source oven to the process system, should be as short as possible and heated. A positive temperature gradient should be maintained on the components and plumbing from the source oven to the process chamber to prevent condensation. Condensation causes oscillation in flow stability or non-repeatability in film deposition rates. Similar problems may occur in bubbler systems if one is not careful.
1150C Vapor Mass Flow Controller Components
The 1152C consists of a fixed flow element and two capacitance manometers for flow measurement, with a proportioning solenoid control valve for flow control (U.S. Patent No. 4,679,585). All components and associated circuitry are contained within a compact temperature-controlled assembly with a temperature status LED and relay to indicate when temperature is in range. A temperature sensor and voltage output is available to indicate that the controller is at an elevated temperature to prevent vapor condensation within the mechanical assembly The critical pressure measurements in the 1152C are made by the reliable Baratron® capacitance manometers. Components are assembled to the flow element body using nickel seals. The environment around the mechanical assembly of control valve, flow element, and sensor is temperature controlled up to 100°C (temperature control to 150°C is available upon request). Above the mechanical assembly in the 1152C is the pressure sensor signal conditioning and P.I.D. control loop circuitry. The valve driver output of the controller is sent to a solenoid-type proportioning valve upstream of the flow element to deliver the desired amount of gas flow to the process chamber.