Cryo-Evaporator Operation Cara Ricci November 25, 2003 Thin Film Deposition THE UNIVERSITY OF TEXAS AT DALLAS ERIK JOHNSON SCHOOL OF ENGINEERING DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 1 of 28
Cryo-Evaporator Operation Cara Ricci November 25, 2003 Thin Film Deposition TABLE OF CONTENTS 1 INTRODUCTION...3 1.1 Purpose...3 1.2 Scope...3 1.3 Definitions...3 1.4 Cryo-evaporator Functionality...5 2 METAL DEPOSITION BY CRYO-EVAPORATION...6 2.1 Procedure...6 DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 2 of 28
1 INTRODUCTION 1.1 Purpose This document describes the procedure for depositing metals with the Cryo-evaporator. The Cryo-evaporator is used to deposit various metals (i.e. gold, silver, chromium, zinc, and others) onto a substrate material like silicon. 1.2 Scope This document describes metal deposition using the Cryo-evaporator and is limited to the process of metal evaporation; the types of metals deposited by the Cryo-evaporator are beyond the scope of this document. 1.3 Definitions Angstrom Atmosphere Bell Jar Chamber (Å) A unit used to measure very small lengths, such as wave length. Equal to 10-10 m Unit of pressure that corresponds to standard atmospheric pressure. It is taken as the pressure that will support a column of mercury 760 mm high. 1 std atm = 750 torr = 101,325 pascal Apparatus that encloses the vacuum chamber; a container that is closed at the top and opens at the bottom The part of the vacuum system where the process is performed Cryopump A high vacuum pump, operates in the pressure range of 10-3 - 10-8 torr Emission A substance (or substances) discharged into the air Evaporation The process that takes place when a solid or liquid become a gas HiVac High Vac is a term used to describe a good vacuum (10-3 - 10-8 torr), in which most of the gas has been removed HiVac Valve Large diameter valve usually placed between the vacuum chamber and the vacuum pumps; used to isolate the chamber from the pumps when it is necessary to work in the chamber. Ion An atom or group of atoms that carries a positive or negative electric charge as a result of having lost or gained one or more electrons (Ionization) Ion Gauge See Thermionic Vacuum Gauge Rough Pump A pump which functions in the rough vacuum range Rough Vacuum Term that is used to describe a vacuum in which an appreciable amount of gas is still remaining (759 10-3 torr), also referred to as Low Vac or Rough Vac DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 3 of 28
Roughing Valve Valve used for the initial evacuation of a gas (or gases) in a vacuum chamber, generally used to create a rough vacuum (just below atmosphere to 10-3 Torr) Substrate The material on which something is to be made Thermionic Vacuum Gauge Emits electrons off a hot filament; emitted electrons are attracted to a positive grid, electrons en route may collide with and ionize gas molecules and release more electrons, the positively charged ionized gas molecules produce an ion current proportional to the vacuum level; also referred to as an Ion Gauge or a Hot Cathode Ion Gauge (The latter term being a bit misleading since it is actually the filament which becomes hot while the cathode becomes merely warm) Torr Unit of pressure. 1 torr = 1 mm of Hg = 133.3 Pa Vacuum Used to describe any pressure less than atmospheric pressure Vent Valve Valve used to let air or other gases back into the vacuum chamber Wafer A thin slice of semiconductor (such as silicon) used as a base for an electronic component, or substrate. DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 4 of 28
OVERVIEW 1.4 Cryo-evaporator Functionality The Cryo-evaporator is used for coating various substrates, including silicon and glass, with a thin metallic film. Many types of metals can be evaporated including Ag, Al, Au, Cr, Cu, Ti and others. This process includes heating a desired metal in a vacuum until it evaporates. The evaporated stream of metallic vapor covers the substrate with a smooth coating; the thickness of the deposited metal film must be monitored continuously. One particular advantage of the cryoevaporator is the cryopump. The cryopump pumps the chamber down to a high vacuum range by decreasing the temperature until the gases freeze. This process of trapping and storing gases is very clean because it is oil free and uses no moving parts in vacuum. Note: Be sure to always wear polyethylene or powder-free latex gloves when using the cryoevaporator or touching any samples in or inside of the chamber. Never touch any part of the chamber with your bare skin as this will result in chemical contamination inside the chamber that can damage future depositions. DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 5 of 28
2 METAL DEPOSITION BY CRYO-EVAPORATION The method described below is a general procedure describing the process of metal deposition with the Cryo-evaporator. 2.1 Procedure 1. Verify that the Hi-Vac valve is closed; as seen in Figure 1, the handle should be turned in a clock-wise direction until parallel with the floor. Figure 1 Hi-Vac Valve (Closed) 2. Verify that the Pneumatic Roughing valve is also closed. Both the red protective cover and metal lever should be in the down position (Figure 2). Figure 2 - Pneumatic Roughing Valve (Closed) DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 6 of 28
3. Next, vent the chamber to raise the pressure to atmosphere ( Figure 3): 1. Remove the front panel located beneath chamber by pulling down on the two metal rings located on the top left and right sides ( Figure 3) Figure 3 - Front Panel Latches (marked by arrows) DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 7 of 28
2. Find the Vent Valve, a black faucet like knob, located on the left hand side beneath the chamber table (Figure 4). Figure 4 - Vent Valve Located inside the front panel below and to the left of the Bell Jar Base 3. Turn the knob counter clockwise (to your left) to open; you should be able to feel suction at the opposite end of the of the valve opening 5. Check the Cryogenics Temperature Indicator (CTI) located on the right side of the chamber, it should read 12 14 o C ; if the temperature increases, check the HI VAC valve to make sure it is completely closed Note: If the HIVAC valve is completely closed and the temperature reads outside of the 12 14 o C range; contact support personnel in the clean room immediately for assistance 6. Continue to turn the valve until a slight whistling sound is heard, this indicates that the chamber pressure is increasing. Once the pressure begins to increase, stop turning the knob and wait approximately 2-3 minutes 7. Once the pressure has reached atmosphere level, completely open the vent valve (counterclockwise) as seen in Figure 4 DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 8 of 28
4. Open the chamber (Figure 5) by moving the lever (indicated by the arrow) forward, or away from you, to raise the Bell Jar. Figure 5 Lever used to position the Bell Jar 5. Once the Bell Jar is open, close the vent valve (Figure 4 page 8) by turning the knob clockwise until the knob stops. 6. Apply power to the Inficon as seen in Figure 6. OFF ON Figure 6 Inficon film thickness monitor 7. Check for the XTAL indicator light, if the indicator is blinking, the crystal is bad. Note: If the crystal is bad, it will need to be changed; contact support personnel in the clean room for assistance. DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 9 of 28
If the XTAL indicator is not blinking, the crystal is good and ready for use. 8. Place your wafer on the substrate mounting platter and secure it by fastening the metal clips as shown in Figure 7. Note: You need to use the 5/16 th inch socket wrench to fasten the clips. Figure 7 - Substrate Mounting Platter 10. To ensure that the surface of the wafer is clean, use the compressed N 2 gun, located to the left of the RIE etching machine, to blast any debris from the surface. 11. Before lowering the Bell Jar, turn the metal mounting platter upside down so holes match up and wafer faces the bottom of the chamber (Figure 8). DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 10 of 28
Figure 8 - Aligning the Substrate Mounting Platter 12. Once the metal mounting platter is in place, lower the Bell Jar by moving the lever switch on the left hand side of the chamber table (as seen Figure 5 on page 9, marked by the arrow) back (towards you). Guide the chamber downward and ensure it is sealed well when closed. 13. Now that the chamber is closed, check to make sure that the Vent Value is completely closed (turned clockwise) as seen in Figure 9. Figure 9 - Vent Valve (Close) 14. When the Vent Valve is closed, replace the Front Access Panel as shown in Figure 10 DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 11 of 28
Figure 10 - Front Access Panel 15. Before opening the Roughing Valve, check the Hi Vac Valve and make sure it is tightly closed (turned completely to the right) as demonstrated by arrow in Figure 1 16. Next, open the Pneumatic Roughing Valve by raising the red toggle protector and lifting the metal lever up as seen in Figure 11. Figure 11 - Pneumatic Roughing Valve (Open) 17. Wait for pressure to drop to 5.0E-2 Torr or lower as indicated by the TC1 readout on the Varian. (Figure 12) Figure 12 - Varina SenTorr (TC1 readout) 18. When the pressure has reached the specified value, close the roughing valve by pushing the red toggle protector down (Figure 13). DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 12 of 28
Figure 13 - Pneumatic Roughing Valve (Close) 19. When the Pneumatic Roughing Valve is closed, open the Hi Vac Valve all the way by turning the knob counter clockwise (to your left) as seen in Figure 14. Figure 14 - Hi Vac Valve (Open) 20. Log the time at which you opened the Hi Vac Valve. DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 13 of 28
Figure 15 - Log Book DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 14 of 28
21. On the Varian SenTorr, push the EMIS button (Figure 16) to turn on the Thermionic Vacuum Gauge (Figure 17). Figure 16 - Varian SenTorr Figure 17 - Thermionic Vacuum Gauge 22. Wait for the IG readout (highlighted in blue) to reach 4.0E-6, this takes approximately 30-40 minutes. 23. Once the IG has reached the specified value, program the Inficon (Figure 18) as shown below: DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 15 of 28
Figure 18 Inficon - film thickness monitor 1. Press the Program button (indicated by the red arrow) 2. Next, press the Thickness 2 button and enter a value for Thickness 2 followed by the Enter button (highlighted in blue) 3. Press the Thickness 1 button and enter a value (usually the same as Thickness 2 ) and press Enter 4. Next, press the Time button and enter a value for Time (typically 9999 ) and press Enter 5. Press the Density button and enter a value for Density (this depends on the metal you are depositing and should be obtained from the Bulk densities and Z Values table) and press Enter 6. Press the Z Ratio button and enter a value for Z Ratio (again, this depends on the metal you are depositing, obtain from the Bulk Densities and Z Values table) and press Enter 7. Finally, press the Tooling button and enter a value for Tooling (typically 100 ), press Enter 24. Open the water valve (located behind Indy) by turning the valve to your left until the handle is parallel with the water line as shown in Figure 19 DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 16 of 28
Figure 19 - Water Valve (Open) 25. Turn on the circuit breaker by flipping the switch up (you will hear a loud click); the box is located on the wall to the right of the Cryo-evaporator as seen Figure 20. Figure 20 - Circuit Breaker (On) 26. Apply power to the Airco Temscal Power Supply (Rolling Power Supply) by flipping the switch up, this circuit breaker is located on the front panel of the rolling power supply (Figure 21). DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 17 of 28
Figure 21 - Airco Temescal (Rolling) Power Supply (On) 27. Start the CV-8 Airco Temescal located above the power supply (Figure 22) by performing the following steps: Figure 22 - CV-8 AircoTemescal 1. Turn the Key to the On position; the P.C. cards & Keylock and HV OFF lights should come on (highlighted in blue) o Note: You can zero out on the Inficon by pressing the Zero button on the Inficon. 2. On the CV-8, turn the Emission Control knob (highlighted in green), located on the right side, to zero 3. Press the H.V. ON button (highlighted in orange) and hold for 1 second DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 18 of 28
4. Press the Gun #1 Fil. On button (highlighted in yellow) 5. Turn the Emission Control knob (in green) to desired setting which is dependent on the metal you are depositing 28. Look through the window in the bell jar, a light purple glow in the crucible in the chamber indicates the metal is heating up as seen in Figure 23. Figure 23 - Chamber Crucible 29. Check the Angstrom readout on the Inficon and adjust your deposition rate (Angstrom/sec value) by moving the Emission Control knob on the CV-8 Airco Temescal to reach your target deposition rate (Figure 24). (Note: Use caution when adjusting the Emission Control knob because a small change with the knob will result in a fairly significant change in your deposition rate (Angstroms/sec)). Angstroms/sec Angstroms Figure 24 - Angstrom Readout - Inficon 30. When you reach your desired readout on the Inficon, press the Zero button (highlighted in blue) to zero-out the Inficon. 31. Open the chamber shutter (Figure 25) to begin deposition: DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 19 of 28
Figure 25 - Shutter Control (Open) 1. The shutter is controlled by a rubber tube located below the bell jar. 2. Turn the tube Clockwise (to the right) to open the shutter as seen in Figure 25 and hold it open 32. With the shutter open and out of the way, allow the evaporating metal to deposit onto the substrate to the desired thickness. 33. On the Inficon (Figure 24, page 18), for most metals you should keep your deposition rate at approximately 1-1.5 Angstroms/sec, you will get a more even coating if you run it slowly; to be safe keep it below 2 Angstroms/sec 34. Continue to hold the shutter open until you reach you desired thickness. DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 20 of 28
35. Once you are ready to stop depositing metal, perform the following steps: Figure 26 CV-8 Airco Temescal 1. Press the H.V. Off button on the CV-8 Airco Temescal (Figure 26, highlighted in blue) and close the Shutter (see Figure 25 - Shutter Control on page 18) at the same time (to close the shutter, turn the tubing counter counterclockwise or to your left) o Turning off the High Voltage stops the electron beam from heating the metal and closing the shutter physically stops any further deposition. 2. Push the Gun #1 Fil. Off button on the Airco Temescal (Figure 26, highlighted in yellow) 3. Return the Emission Control knob to Zero (Figure 26, highlighted in green) 4. Turn the key on the Airco Temescal to the off position (this disables the high voltage) 5. Turn the Emis Ion Gauge off on the Varian (see Figure 16 - Varian SenTorr on page 15) DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 21 of 28
6. Remove power from the Inficon as seen below in Figure 27 OFF ON Figure 27 - Inficon 36. Allow the system to cool for 15-20 minutes. 37. After the system has cooled, turn the Main Power off on the rolling power supply by flipping the lever down as shown in Figure 28. Figure 28 - Main Power - Rolling Power Supply (Off) DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 22 of 28
39. Turn off water valve (located behind Indy) by turning the valve to your right until the handle is perpendicular with the water line (Figure 29) Figure 29 - Water Valve (Off) 40. Turn off power at main circuit breaker Figure 30 - Circuit Breaker (Off) DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 23 of 28
41. Close the HiVac valve (clockwise), it is important to make sure it is completely closed so apply approximately 50 pounds of force to the lever; you want it to be snug but not too tight. Figure 31 - Hi-Vac Valve 42. Remove the front panel again by pulling downward on the rings and lifting up on the panel (Figure 32). Figure 32 - Front Panel Latches (marked by arrows) DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 24 of 28
43. Open the Vent Valve by turning the knob counter clockwise (or to your left) until you hear a slight hissing sound, then turn it two or three more times as seen in Figure 33. Wait for the chamber to vent, the hissing will stop when it has reached Atmospheric pressure. Figure 33 - Vent Valve (Open) 44. Push the lever forward to open the bell jar (Figure 34). When the bell jar has completely opened you can rotate it to the left out of your way. Figure 34 - Opening the Bell Jar DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 25 of 28
45. Remove the metal platter from the chamber by lifting it from the three metal prongs on which it is mounted (as seen in Figure 35), and set it on the table to the left of the machine. Figure 35 - Metal Platter 46. Check the glass slides that cover the window of the bell jar, if the slides are no longer transparent, they will need to be replaced. 47. Close the Bell Jar by pulling the lever backwards (indicated by the red arrow in Figure 36) Figure 36 - Bell Jar in the Closed Position DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 26 of 28
48. Next, close the Vent Valve by turning it clockwise (right), as seen in Figure 37 Figure 37 - Vent Valve (Close) 49. Open the Roughing Valve by lifting the red toggle protector and metal lever up (Figure 38). Figure 38 - Pneumatic Roughing Valve (Open) DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 27 of 28
50. Pump the system down to 2E-2 torr (Figure 39 shown in blue). Figure 39 - Varian SenTorr 51. Close Roughing Valve (Figure 40). Figure 40 - Pneumatic Roughing Valve (Close) 52. End of procedure. DOCUMENT NUMBER: FA2003-TF-008 EDITION: 1.1 PAGE: 28 of 28