Papers

AVS2004 Session EW-TuL: Innovations in Vacuum Techniques and Measurements

Tuesday, November 16, 2004 12:20 PM in Room Exhibit Hall B

Tuesday Afternoon

Start	Invited?	Item
12:20 PM		EW-TuL-2 Residual Gas and Improved Pressure Control Resolution using a Cryocooled Water-Pumping Throttle Valve H. Grover (MeiVac Inc.); N. GurArye (Ricor) Precise pressure and residual gas control are critical to quality, yield and profitability. Contamination control and process response/recovery advantages of Downstream versus Upstream pressure control will be discussed using multiple feedback and throttling schemes. Valve geometry and actuation methods determine maximum and minimum conductance, as well as, linearity and resolution of the throttling curve. Concepts of linear throttling control and differential pumping of residual gas will be offered including test data correlated with theoretical calculations. Throttling normally restricts flow of all gaseous components. Experimental data will be presented offering differential pumping of condensables (primarily water vapor) while throttling process gases with a high differential pumping ratio. Advantages and disadvantage of Meissner, flow through cryo water vapor pumps and appendage cryo water vapor pumps will be technically and economically compared to a combined package cryocooled water pumping throttle valve. Species range specific condensable pumping control will be presented using a unique externally controlled servo motor driven cold head instead of the conventional pneumatic driven cryo mechanism. Practical examples will be displayed using advanced cryo technology that allows self-contained cryo cooled throttle valves with no cryo compressor required.
1:00 PM		EW-TuL-4 A Shuttle System for Rapidly Transfering Components Into and Out of a Vacuum Chamber R.E. Trillwood (Electron Beam Engineering Inc.) Shuttle System for transferring parts into and out of a high vacuum system. The Shuttle System was invented in 1988 to enable the rapid production of parts with an electron beam welding machine. Traditionally multiple fixtures are used to load several parts into the vacuum chamber; this amortizes the evacuation time over the number of parts. However the disadvantages are that it is a "batch" operation and it does not eliminate the evacuation time from the process. The Shuttle consists of a piston and cylinder normally mounted on the side of the vacuum work chamber and fitted with a pre-pumping stage. The part, or parts for processing are loaded into a breech cut into the piston and transferred into the chamber, stopping momentarily at the pre-pumping stage. The uniqueness of the system is in the displacement of the seals in the piston and cylinder, which facilitates transfer of parts without a pressure rise in the work chamber. Since the Shuttle volume is usually small compared to the work chamber volume there is the added advantage of "volume sharing" to dilute any residual pressure in the breech as it is transferred. For example the pre pumping stage is typically at a pressure of 100 mili torr but with "volume sharing" as the breech enters the larger work chamber there is no noticeable pressure rise. If a higher level of vacuum is required then it is only necessary to provide a higher level in the pre pumping stage. Today there are several Shuttles in operation, which have produced in excess of a million welded parts with production rates of over 250 parts per hour. It is anticipated that there are many more vacuum applications in industry that could use this invention. Richard Trillwood Patents "Shuttle system for rapidly manipulating a work piece into and out of an atmospherically controlled chamber for doing work thereon in the chamber" Patent number 5,062,758 and4,968,206. Trillwood 4/27/2004.
1:20 PM		EW-TuL-5 Triple Gauge, A New Combination Vacuum Gauge M. Wuest, R. Enderes, U. Waelchli (INFICON Ltd, Liechtenstein) We have developed a new type of combination vacuum total pressure gauge. The gauge combines a Bayard-Alpert, a Pirani and, as a novelty, a capacitive diaphragm gauge (CDG) in one housing of less than 30 mm diameter and 60 mm in length. Up to now this was the size of the most modern Pirani Bayard-Alpert gauges. The gauge has a large measurement range from 5E-10 mbar to 1500 mbar. Compared to the previous Bayard-Alpert Pirani combination gauge, the addition of a CDG provides gas type independent pressure measurement above 10 mbar. This solves venting problems with different gas types such as argon or helium and is therefore ideal for load lock applications. The integrated Pirani sensor protects the yttrium oxide coated iridium filament of the Bayard-Alpert gauge from premature burnout and bridges the pressure range between the Bayard-Alpert (5E-10 mbar to 1E-2 mbar) and the CDG measurement range (10-1500 mbar). This new combination is realized thanks to a novel miniature ceramic CDG. The 11 mm diameter alumina CDG has a reference vacuum in the 1E-4 mbar range. The pressure is sensed by measuring the deflection of an 80 micrometer thick diaphragm over a gap distance of 15 micrometer. The resolution is 0.2% of measured value over a range of 100-1500 mbar. In addition, one version of the gauge includes an absolute atmospheric pressure sensor for even more accurate load-lock application. A combination gauge saves cost for the original equipment manufacturer as it reduces system requirements such as the number of flanges and cables required as well as software interfaces and testing time. We will give an overview of the sensing principles and sensors involved and present pertinent specifications of the gauge.
1:40 PM		EW-TuL-6 Impact of Chamber Matching and Process Capability Through Flow Measurement and Adjustment S.A. Tison, D. Leet, C. Adcock, S. Lu (Mykrolis Corporation) To ensure process transparency when replacing mass flow controllers (MFC) or when employing new types of mass flow controllers in a particular process, it is often desired to have the flow rate of the replacement MFC match the flow rate of the previously installed MFCs. This can be accomplished in one of two ways. The first way is the most traditional and relies on the inherent accuracy of the MFCs, calibrated traceable to national standards. The second method relies upon an alternate standard, often the tool flow verification methodology. To accomplish the second method requires that the replacement MFC must effectively be recalibrated â?oon-toolâ? to match the output of the previous MFC. The most common method to achieve this is to use the process tool as the flow measurement standard and obtain flow data on the MFC prior to removal. After the replacement MFC is installed the same data is taken and the new MFC is adjusted to achieve the same output as previously determined with the original MFC. In addition to process transparency, the replacement or a new MFC may be adjusted on tool to ensure that the flow measurements of the MFC agrees with the process tool flow measurements to within a specified tolerance. Inherent to the technique of adjusting the MFC on the tool is the belief that the flow measurement as established by the tool is the best metric to improve process repeatability and reproducibility. This paper will not attempt to validate this claim, but focuses on how these two techniques are implemented with digital mass flow controllers and process implications.