1150C Mass-Flo® Vapor Source Mass Flow Controllers are pressure based measurement and control systems designed to meter and control vapor from low vapor pressure liquid and solid sources directly, without the need of a carrier gas using viscous flow through a choked orifice.
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.
The 1150C is based on viscous choked flow technology. The equation describing choked flow through an orifice is Q = CP1 where Q is mass flow, C is a constant, and P1 is upstream pressure. The equation shows how the flow through a choked orifice is related to the pressure upstream of that orifice. An absolute pressure measurement before the orifice is required. Choked flow is achieved when the upstream pressure (P1) is approximately twice the downstream pressure (P2). This condition can limit the dynamic range of accurate measurement; however, the control range repeatability is not compromised. Since the upstream pressure must be twice the downstream pressure, this system is best suited for applications in which processing system pressure is less than a few Torr.
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.
The 1150C vapor mass flow controller consists of a fixed flow element and one 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 1150C controller is at an elevated temperature to prevent vapor condensation within the mechanical assembly. The critical pressure measurement in the 1150C is made by the reliable Baratron® capacitance manometer. 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 1150C 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.
|1||+15 VDC Input|
|3||-15 VDC Input|
|4||Temperature Relay (N.O.)|
|5||Temperature Relay Common|
|8||Temperature Relay (N.C.)|
|1||Valve Test Point|
|2||Flow Signal Output|
|3||Valve Close Override|
|4||Valve Open Override|
|8||Set Point Input|
|13||P1 Test Point|
|14||P2 Test Point (1152C only)|