Temescal BJD-1800 E-Beam Evaporator 1 System Overview - Cryo-pumped for typical base pressures in the low 10e-7 Torr range. - Four pockets in the rotating hearth of the electron gun which allows deposition of up to four materials under one pump down. - Thickness and deposition rate are controlled by an Inficon IC/5 Deposition Controller. - Nano3 provides a wide variety of materials for e-beam deposition. - This system is a mostly MANUAL system. Most parameters need to be adjusted by the user. - Only high-vacuum compatible samples are permitted in this system. Zinc, brass, plastic substrates, tape (expect for Nano3 supplied Kapton tape) are NOT permitted. Photoresists MUST be hard baked. 1
Upon Approaching the System Figure 1 Figure 2 - Make sure the cryo pump temperature is 20K or less on the temperature gauge (Figure 1). If not, stop and notify staff. - Make sure that the IG1 pressure is less that 1 x 10^-6 Torr ( High vacuum ; Figure 2). If not, stop and notify staff. Users are required to leave the system at high vacuum after deposition and are not allowed to leave until the pressure has dropped to 1 x 10^-6 Torr or less. - Look at the logbook (Figure 3, next page) and make sure the person ahead of you has finished and signed out. Legibly fill in your name (first and last name), the date, the load time, and the material you plan to deposit. 2
Upon Approaching the System Figure 3 3
Figure 4 Figure 5 Venting the System - Make sure the Vent Switch on the Vacuum Control is in the Auto (up) position (see left red arrow in Figure 4). - Push the Auto Stop Button (right red arrow in Figure 4). The system will automatically vent (it will close the high vac valve and roughing valve, and open the high vac vent valve). As the system vents, the IG1 gauge (Figure 5) will turn off, and the PG1 gauge will begin to display a pressure reading, slowly increasing to ~760 Torr (atmospheric pressure). - The Ion Gauge ( IG1 ) reads pressures between 10^-4 Torr and 10^-12 Torr, and the Pirani Gauge ( PG1 ) can reads pressures from slightly above atmospheric to 10^-4 Torr. 4
Venting the System View Port Slide Crystal Monitor Top Bottom - Once the system is vented you will open the lid. Be careful as it is heavy. - Once the lid is open (Figure 6), check that a large clean glass slide has been installed over the viewport. This protects the viewport from being coated with material, which would make it impossibly to view inside the system from outside once the system in again evacuated. Do not forget the glass slide; a coated viewport will need to be replaced and is very expensive. - If you have to replace the slide because it is coated, be careful that you insert the new slide correctly, and the corner does not get caught on the viewport. Figure 6 5
Checking the Quartz Crystal Monitor 2 1 3 Figure 7 Figure 8 - The Quartz Crystal Monitor (QCM) is used to measure the deposition rate and the thickness deposited. - Look at the IC/5 Controller and the keypad next to it (Figure 7). Then press the F2 Button next to Sensors. - In the sensors screen, you will see two lines, the first one is the only one that matters. Look at the LIFE column (Figure 8), the reading should be between 0-10, if it is over 10, the crystal needs to be replaced. - Life is a measure of the amount of material deposit on the surface of the crystal. Increasing thickness of deposit affects the accuracy of the measurement. The loss in accuracy is minimal up to Life readings of 10. Heavier materials, such as nickel, will drain the crystal life faster than lighter elements, such as aluminum. - If the crystal needs to be replaced, notify staff. - Users ARE NOT allowed to change the crystal on this system. - Press the F6 button next to Operate to return to the home screen (Figure 7). - Note that the code xtal fail will show on the bottom right of both the home and sensors screen if the crystal is improperly seated or broken. This also means the crystal needs to be replaced. 6
Checking the Materials Open Close Figure 9 Figure 10 - Move the shutter control switch to OPEN to open the shutter (Figure 9). Look into the chamber. - Verify that the material in the crucible in the indicated pocket (Figure 10) matches with the magnetic tag on the door (Figure 11, next page). The material is inscribed on the bottom of the crucible (Figure 12, next page). - If they do not match or you want a different material, look for the crucibles and tags for E-Beam 1 in the cage opposite the machines. NOTE that E-Beams 1 and 2 have different crucibles and tags. E-Beam 1 takes larger crucibles in general but actually has 3 sizes of crucibles. 7
Checking the Materials Figure 11 Figure 12 - Once you are satisfied with the material, turn the turret source selector CLOCKWISE to the next crucible; this means if you are starting at A, then go to B, check the crucible, then go to C, check the crucible, then go to D, check the crucible, and then go back to A (Figure 9, previous page). - DO NOT turn the turret selector backwards (COUNTERCLOCKWISE) as you will damage the selector. - Verify or change each material as desired and make sure you put up the corresponding tag for that material. Put unwanted materials back in their respective empty cases. - Be efficient and put materials into turret pockets in the same order you will deposit them in. - When you finish, close the shutter by setting the switch to close (Figure 9). - The only two materials not inscribed on the bottom of the crucible are chromium and gold. Chromium comes in greyish green pieces which evaporate individually and do not melt. Gold is colored differently than the other metals but behaves similarly as the others during evaporation. 8
Default Sample Plate Loading Your Sample (Default Sample Plate) Clips Figure 13 Figure 14 - The default sample plate is shown in Figure 13. Your sample will be attached to the plate facing downward. - We recommend that all samples be clipped to the plate with screws and clips. Use of Kapton tape is not explicitly forbidden but it is not recommended (Figure 14). - We advise against the use of Kapton tape because its adhesive will outgas under vacuum (especially as the sample heats up during evaporation) and contribute contaminants to your sample. Furthermore, as the sample temperature increases, the adhesion of the tape may also sufficiently weaken for your sample to fall off the holder. At minimum, the reduced adhesion will affect the heat transfer from your sample to the sample holder, causing it to overheat more readily. - If you do use Kapton tape, you MUST clean the holder of all tape residue after use. 9
Loading Your Sample (Alternate Sample Holders) Sample Holder With Thermocouple Small Sample Holder Heat Shield Figure 15 Figure 16 - There are two other sample plates/holders that can be used in E-Beam 1. The plate shown in Figure 15 has a round cut-out in the center to hold small sample holders (not provided). The small sample holders can, for example, be configured to mount samples at angles. - The sample holder shown in Figure 16 is fitted with a thermocouple for temperature measurement. This holder also allows you to cool samples with coolant. The heat shield helps to reduce the heat load on the holder during evaporation by lowering the heat reflected from the sample lid. Samples mounted to this particular holder are further away from the electron gun, and real deposition rate/thickness is about ½ lower than recorded by the IC/5 controller. You should to a test run to determine the exact correction factor. - Contact Nano3 staff for details on how to use these alternate sample holders. 10
Pumping Down the System Auto Start Auto Stop Figure 17 Figure 18 - Before pumping down the system, check the sealing surface of the lid and the o-ring by visually inspecting for debris (usually shiny small metal flakes if any) and running a clean glove along the surfaces. - If something needs to be cleaned off, use one of the soft polyester cleanroom wipes NOT the stiffer, polycellulose cleanroom wipes (these would shed particles on the o-ring). - DO NOT USE ANY SOLVENT, only dry wipes. - Close the lid of the system gently, make sure it is seated well, and then turn the mechanical pump switch on by pulling it up (Figure 17). - Wait five to ten seconds, then press Auto Start (Figure 18). Waiting prevents an imbalance of pressures in the roughing line and the chamber, which can cause roughing pump oil to leak back into and contaminate the system. 11
Pumping Down the System Numbers in small font indicates gauge warmup Figure 19 Figure 20 - The system will rough pump down to about 62-63 mtorr (displayed on the PG1 readout, Figure 19), at which point the system will close the roughing valve. The system will then sit idle for about 5 seconds to perform a leak check. If the system drifts above 70 mtorr (the leak test failed), the system will repeat the leak check. This process will repeat over and over, and so the user must vent the system by pressing auto stop (Figure 18, previous slide), wait until the system is vented, and then check the o-ring and sealing surface again before attempting to pump the system again. - When the system passes the check, the high vacuum valve will automatically open, and the PG1 reading will drop to 0 (Figure 19). At the same time, IG1 display will start to display numbers in small fonts as the gauge warms up. When the IG1 readout switches to large font and displays a pressure reading, turn off (down) the mechanical pump switch (Figure 20). - In general, the system should take about 20 minutes to fully pump down. If the system was open for an extended period of time, or if samples outgas, this time will increase. 12
Material Properties - The system pressure will affect the qualities of the evaporated films. With lower systems pressures, fewer contaminants from residual gas (mostly water) will be incorporated into the deposited films. - Wait for the system pressure to drop below 9x10^-7 Torr before evaporating any material. When you evaporate highly reactive materials such as titanium or chromium, you will notice that the pressure rapidly drops during deposition because the deposited material will readily bind residual gas molecules. During evaporation of less reactive materials, such as gold, silver, etc., you will not tend to see this. Titanium or chromium are frequently used as adhesion layers for subsequently evaporated materials, and you may want to let the pressure drop as low as possible to make sure that the adhesion layer is not oxidized before you begin evaporation of the second material. - For materials with high melting points more electron beam power must typically be used in order to evaporate. This tends to increase the chamber temperature, causing a pressure increase and decreasing film quality. You should wait to attain a pressure as low as possible before evaporation of these materials (below 1x10^-7 Torr). - The electron beam power used will affect surface roughness, density, grain size, etc. Typically, deposition at higher rates (i.e. more power, e.g. 4 angstroms/sec) results in rougher surfaces and lower film density. Deposition at lower rates (i.e. less power, e.g. 0.5 angstroms/sec) tends to result in smoother, denser films. - You are encouraged to run dummy samples in the system to optimize film quality for your application. 13
Programing the Deposition Controller Active Process 2 1 Figure 21 Figure 22-1. WHILE THE MACHINE IS PUMPING DOWN, look at the IC/5 Deposition Controller and the keypad next to it. Then press the F6 Button next to Program (Figure 21). - 2. Then press F2 next to Process Directory (Figure 22). - 3. Use the up and down arrow keys to scroll through the materials and select the material you want to run. Scrolling through the bottom takes you back to the top of the page. If your material is not listed on this page, press F1 next to Page Forward to see more pages of materials (Figures 23 and 24, both on next page). 14
Programing the Deposition Controller 3 4 5 Figure 23 Figure 24-4. Once the material is selected, press F4 next to Select Active Process. The active process listed in the upper right hand corner of the screen should now reflect the process that was selected (Figures 22, on previous page, and 24). - 5. Press F6 for Program and F6 again for Operate to return to the home page (Figure 24). - Be sure the home page reads the material that was selected in the middle top, and be sure the material in question is in the turret selected (turn the turret to it if needed). Do not forget to turn the turret to the current material when depositing different materials in a row. 15
Turning on the Beam Power Switch Figure 25 Figure 26 - Now that the pressure is correct, the deposition process can begin. - Turn on the main power circuit breaker switch (lift up until it clicks) on the high voltage power supply next to the system. Note that this might take a forceful touch (Figures 25 and 26). - Make sure you can feel or hear the fan turn on inside the grate on top of the power supply. This fan cools the power coils and is essential. If it does not turn on, turn off the power switch (press down) and notify staff immediately. DO NOT continue the deposition process, you will damage the system. 16
Turning on the Beam Interlock Switches Air Key Figure 27 - Go to the High Voltage Control and turn the key to the On position (Figure 27). - ALL six buttons above the key should light up immediately. These are interlock switches which indicate faults in specific parts of the system. In general, when the key is turned, the first light to turn off is the core fault. DO NOT continue the deposition process if ANY of the lights do not turn on. Turn the key to the Off position, turn the power supply switch to off and notify staff (Figure 27). - If you find that the only light off is the Air light (indicative of an issue with compressed air supply to the system), wait several minutes to see whether the issue resolves itself. If not, turn the power supply switch to off and notify staff. 17
Turning on the Beam Voltage Gauge Interlock Switches HV On Gun 1 Fil On Gun 1 Fil Off Figure 28 Figure 29 - Press firmly and hold the red HV On button ( High Voltage Control, Figure 28) for 2-3 seconds to turn on the high voltage. You should hear a click when you release the button. The needle on the voltage gauge should now swing up to between 9-10 kv. - WARNING, once HV is on and the voltage gauge displays 9-10kV the user must never leave the system until HV is turned off. - Press firmly and hold the red Gun 1 Fil On button ( Gun Control 1, Figure 29) for 2-3 seconds to turn on the gun. You should hear a click when you release the button. Again all three interlock switches should light up, if they do not, turn off the gun, the high voltage, and the power source and notify staff. 18
Turning on the Beam Voltage Gauge Emission Current Knob Figure 30 Figure 31 - Check through the upper viewport that the chamber is now illuminated by a brownish/yellow light (Figure 30). If this is not the case, but the interlock switches are all on (for high voltage and the gun), then the Gun Fil On switch was not depressed firmly enough. Press Gun Fil Off, wait 2-3 seconds, the press Gun Fil On more firmly and check the interlocks and viewport again (Figures 29, previous page, and 30). - Using ONLY THE INNER Gun Emission Current knob slowly increase the gun emission until the needle on the current gauge above the knob reads 0.4 and wait 1 minute (Figure 31). - Note the IG1 pressure indicated on the pressure controller screen. This is the base pressure which must be recorded in the log book (Figure 32, next page). - Also note that the outer portion of the Emission Current knob will turn slowly on its own as you turn the inner knob, do not directly turn the outer portion of the knob. (Figure 31). 19
Turning on the Beam Figure 32 - After you have waited one minute and recorded the system base pressure, gently and uniformly turn the INNER emission knob again until the gauge reads 0.6. Wait another full minute. Repeat this in increments of 0.2 with 1 minute breaks until you get to 1.0 THEN after the last one minute break, gently turn the INNER emission knob until the gauge reads 1.05 (note that the increment has changed from 0.2 to 0.05). Wait another minute (Figure 31, previous page). - The XYS-8 Sweep Control (Figure 33, next page) is used to position the electron beam inside the crucible and to set up a beam motion pattern ( sweep ) to optimize evaporation. - Once the emission current gauge reads 1.05, make sure that the Long frequency and Lat frequency dials on are set to 1, the lowest frequency possible. This will let you observe the electron beam travel during adjustment. The LATERAL sweep knob ( Lat Sweep in Figure 33) should also be turned all the way counterclockwise (off) by the previous user, with the longitudinal sweep knob ( Long Sweep in Figure 33) left as is. Look through the upper viewport and switch the shutter switch to the Open position. You should see a faint line moving up and down over the crucible (Figure 34, next page). 20
Long Frequency Long Beam Position Beam Long Sweep Figure 33 Long Lat Setting Up the Beam Figure 34 Lat Frequency Lat Beam Position Crucible as seen through viewport Lat Sweep - It is critical that the electron beam is set up correctly in order to avoid possible damage to the system! - NOTE the arrows indicating the directions for the longitudinal and lateral beam adjustments shown in Figure 34. - Adjust both the Longitudinal and Lateral Beam Position knobs until the line formed by the electron beam is centered in the crucible. - If the ends of the beam are outside or touching the inner edges of the crucible, turn the Longitudinal sweep down (counterclockwise) to shrink the line until it is just within the inner edges of the crucible. Likewise, turn Long sweep up if the line does not extend to near the inner edge of the crucible. - Adjust the beam position so that both ends of the beam have equal gaps with the inner edge of the crucible (see Figure 35, next page). 21
Setting Up the Beam Gaps are equal Figure 35 - Ideally, the beam should be close to the inner edge but not touching the edge of the crucible, in order to avoid evaporation of carbon from the crucible. Adjust the beam position until this is accomplished. - Increase (turn clockwise) the lateral sweep knob and so that the beam forms a figure 8 sweep pattern that is evenly centered without touching any of the crucible edges and covers the most area of the material possible (Figure 35). - The Long and Lat frequency settings on the XYS-8 Sweep Control (Figure 33, previous page) can be set as 1, 2, 3.. To 0 (Note that the setting 0 is the highest (NOT lowest) setting!) - Adjust the Long frequency setting to 0 and the Lat frequency to 9. - NOTE: DO NOT USE THE LAT FREQUENCY SETTING OF 0! (Your beam would jump, spatter material, possibly ruin your sample. - The frequencies should not be set to 8 or lower as only the center portion will melt. This would require for the power to be increased for the rest of the material to melt, resulting in higher chamber temperature, higher pressure, and typically poorer film quality. Higher frequency (9 or 10) results in a better coverage of the crucible material by the beam and a more even melt without the need for more power. - BE AWARE that all the materials except chromium have a mirror finish when melted, which results in a reflected beam image to also be visible. Make sure you can tell where the beam truly is. 22
Setting Up the Beam Figure 36 - Also note that different materials will develop convex or concave surfaces when melting which affects the beam reflection. Make sure you take this into account when identifying the beam s reflection in the material vs. the beam itself. - Once the beam has been set up properly, switch the shutter switch back to Close (Figure 36). - Note that the surface of each material will be very lightly contaminated from previous runs. As the material heats up with the shutter open while you set up the beam, this contamination might evaporate and could slightly contaminate your sample. Efficient set up of the beam will minimize the possibility of light contamination. 23
Temperature Properties Figure 37 - Depending on the beam power and material being deposited, the temperature measured at the sample holder can be very high (as high as 220 degrees Celsius). You need to be aware of the properties of the photoresist used on your samples. If the sample temperature is allowed to reach too high a temperature, you may burn the resist. If the temperature becomes equal or close to the hard bake temperature of the resist, the resist can lose viscosity, which can result in wave-like patterns forming on the resist. If the temperature becomes too high, you may lose your sample. You need to make an effort to minimize power used whenever possible in order to avoid a loss of your sample. - The temperature readout for the sample plate is located just behind and to the right of the lid when facing the machine (Figure 37). 24
Beam Properties Figure 38 - In order to ramp up the beam further to correct power for deposition, you must go to the log book (Figure 38) and look at the most recent deposition runs for the materials you will be using. DO NOT look at old deposition values. Look at the max current and deposition rates given by the previous user. If a current seems high for a given deposition rate (angstroms/sec), then it is probably because the beam itself was not setup properly. Always undershoot the values in the log book to compensate for the different beam setups. A slower deposition rate is much more fixable than one that is too high. - NOTE that optimization of film characteristics for your particular application is FULLY the responsibility of the user. 25
Beam Properties - For some materials (e.g. nickel, gold, silver), you need to initially ramp up the current to a HIGHER level then is required for deposition in order to start the melting process. Once the material melts, the deposition rate will suddenly increase GREATLY (going up by more than 1 angstrom/second). At this point, you need to reduce the current using the emission current knob to the level appropriate for your desired deposition rate (Figure 39, next page). - Five magnetic materials are allowed in this system: Nickel, Iron, Cobalt, Permalloy (Nickel-Iron Alloy), and Nickel-Chromium Alloy. The magnetism of these materials will affect the position of the electron beam. Once the material reaches its Curie temperature upon heating, its magnetic properties change, resulting in a sudden shift of the electron beam position. - To correct for this, the beam must be adjusted twice. When the emission current is adjusted initially to a value of 1.05, position the beam (it will be shifted substantially from the position it would have with a non-magnetic material, e.g. titanium). THEN, as you increase the beam emission current, causing the material to heat up, approximately when the material begins to glow orange, the beam will suddenly shift and needs to be readjusted. Start checking the beam position by briefly opening the shutter and adjust the beam when the emission current readout is at a value of 1.3 (you will need to reposition the beam in the opposite direction then when you initially set it up while at an emission current readout value of 1.05). - NOTE, if you initially forget to do the second readjustment, VERY SLOWLY try to reposition the beam to the correct position and adjust for your desired deposition rate. If the beam is out of position, and you were to rapidly re-position it, you would cause the material to pop and splatter, and very likely ruin your sample. 26
Deposition Voltage Gauge Emission Current Knob Close Open Figure 39 Figure 40 - Once you know the appropriate power and deposition rate desired, you may continue to ramp up the power IN INCREMENTS OF 0.05 using the emission control knob with one minute rest between adjustments (Figure 39). - When the appropriate power is reached, open the shutter (shutter switch to open ; Figure 40) so that the crystal monitor and sample are exposed to the evaporating material (and the deposition rate can be read on the IC/5 deposition controller). - NOTE that while the shutter is closed, the rate displayed on the IC/5 might be negative (no material is reaching the crystal monitor). - When the shutter is opened, vibration from the shutter movement will cause a brief immediate negative drop in the rate that is not actually occurring, leading to an error in the recorded thickness reading on the IC/5. Wait with your finger over F1 on the homepage until the rate becomes zero again and immediately press F1 to zero the thickness (Figure 41, next page). - NOTE that the maximum deposition rate allowed is 3 angstroms/sec for aluminum and 4 angstroms/sec for all other materials. DO NOT increase the power beyond this value, you will cause possible damage to the system. 27
Deposition Long Frequency Lat Frequency Long Beam Long Position Sweep Figure 41 Figure 42 Lat Beam Position Lat Sweep - If you observe the deposition rate to be too high or too low, you may adjust the emission control slowly (increments of 0.1 with 1 min breaks between adjustments) WITH the shutter remaining open until you reach the desired rate. It is impossible to control the deposition rate to within 0.1 angstroms/second (Figures 39, previous page, and 41). - For longer deposition runs, you MUST keep watch over the deposition rate as it may change over time due to temperature increase within the chamber. Adjust the emission control dial as explained above to maintain the desired deposition rate. - Periodically verify that the beam is still centered correctly. If it is not, use the Long and Lat beam position knobs to re-center it. Beam drift is more common with longer deposition runs (Figure 42). - At exactly halfway through your deposition time, record the emission current control setting, evaporation (deposition) rate, and pressure during evaporation in the log book (Figure 43, next page). - Close the shutter about one second BEFORE you reach the desired thickness, this compensates for the closing time of the shutter (Figure 40, previous page). 28
Powering Down Voltage Gauge Figure 43 Figure 44 Emission Current Knob Gun Fil On Gun Fil Off - Record the final thickness in the log book (Figure 43). - Ramp down the power in 30 second increments of 0.2 all the way until 0. Ramping down the power slowly helps keep the filament from warping, which keeps the beam straight and focused. Remember that this means ramping down from 0.4 to 0.2 to 0 with 1 minute breaks between adjustments. DO NOT ramp down from 0.4 directly to 0 (Figure 44). - IMPORTANT: IF YOU ARE GOING TO DEPOSIT ANOTHER MATERIAL, FIRST press the Gun Fil Off button, THEN turn the turret to the next material you are depositing and press Gun Fil On. Turning off the gun between switching materials is a failsafe so that in the event of a short circuit in the power supply (where the beam bypasses the controller and emerges at full power) there will be no damage to the copper hearth while the turret is turning (Figure 45, next page). - Hitting the copper hearth with the full beam power while turning could easily cut damage the hearth and flood the chamber with cooling water, causing great damage to the system. - Once you have selected the proper material, make sure to go back and program this material as the active process using the IC/5 deposition controller (See Programing the Materials section, page 14). 29
Powering Down Voltage Gauge HV Off Figure 45 Figure 46 - At this point the process is the same as for the previous material beginning at when you initially pressed Gun Fil On (Page 18). In short, check for the light in the chamber, ramp up the power, deposit, and ramp down and repeat the entire process for as many material depositions as necessary (See Turning on the Beam section, page 18). - IF YOU ARE FINISHED, then continue by pushing Gun 1 Fil OFF (Figure 44, previous page). Then press the HV Off button (voltage should drop back to 0 on the voltage gauge) and turn the key back to the off position (Figure 46). - Then, make sure all frequencies are turned back to 1 and the LATERAL SWEEP dial ONLY is turned off (fully counterclockwise). The longitudinal SWEEP should remain untouched (Figure 47, next page). - Then turn off the high voltage power supply by pressing down the main power circuit breaker switch (Figure 48, next page). 30
Powering Down Long Frequency Lat Frequency Figure 47 Lat Sweep Figure 48 31
Venting and Pumping the System Auto Stop Figure 49 Auto Start - Push the Auto Stop Button on the Vacuum Control (Figure 49). The system will automatically close the high vac valve, make sure the roughing valve is closed, and open the high vac vent valve. As the system vents, the IG1 gauge will turn off, and the PG1 gauge will begin to display a pressure reading. - When the chamber has fully vented, make sure to remove your sample first (to avoid contamination from recent deposition and debris). - Remove any sample holders that are not the built in sample holder (i.e. the one attached to the system lid (Figure 16). - Replace the glass slide over the viewport with a fresh one from the table for the next user, and then repeat the instructions for pumping down the system (See Pumping Down the System section, page 11). - When you turn on the mechanical pump switch and press Auto Start to pump down, record this time as the unload time in the log book (Figure 50 and 51, next page). - STAY with the system until it reaches high vacuum again (until the IG1 gauge has turned on and the pressure reading is 1x10^-6 Torr or below). - MAKE SURE the mechanical pump switch is then turned off, complete the log book entries, and you are finished with the system (Figure 51, next page). Figure 50 32
Venting and Pumping the System Figure 51 33