You must be explicitly authorized to use this machine: tooling on this machine is fragile, expensive, and has a long replacement parts lead-time. Your account will be charged for damage incurred due to misuse, so please double-check your procedures. This SOP does NOT equate to training! It is merely to remind the experienced user of sequencing, and to help the novice plan appropriately.

This machine is very sensitive to particles. You should clean all tooling with 2-propanol and fabwipes prior to Using, should have some spare clean fabwipes available, and put on a new pair of vinyl gloves immediately prior to the bonding sequence, after the cleaning steps. Your wafers should be transported in a closed "bonding box" from their cleaning station, in the teflon boat in which the wafers were cleaned, and you should NEVER use metal tweezers. If you need tweezers, send a pair of teflon tweezers through the wafer clean sequence, draped over the end of the cassette. Be very aware of particles generated by dropping or sliding the wafer, and from your breathing (is your facemask covering your nose?) and clothing.

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EV450 OVERVIEW:

The EV450 aligner is a precision wafer to wafer alignment tool, which can bond wafers or put them in a loadframe for bonding within AB1-PV. Wafers must have low surface roughness, so any CVD, PECVD and many other deposited film types will have to be CMP1d prior to bonding. Also, wafers will have to be rigorously clean, typically to include an RCA clean, immediately prior to bonding, and should not have very large bows. At least one wafer should not be unusually thick, to allow conformal bonding. After bonding, consider Using the IR camera located next to the bonder, to view bond quality, and Using an anneal tube to strengthen the bond. There is a maximum bond stack height, currently about 3 or 4mm, which is tooling dependent.

Start by making sure the aligner x and y verniers are at the 5u mark, and adjust the theta vernier correctly over the white square. Sequentially for all programs, the first wafer is loaded with the bonding surface and alignment marks facing DOWN. It is then aligned via movable bottom mounted CCD cameras in X-direction, and via verniers in theta and Y-direction. Then it is brought into vacuum contact with the bondchuck, and electronically generated crosshairs are then positioned over the still visible crosshairs. If Using Fusion, Thermocompression, or Anodic bonding, you would now insert wafer separation spacers called FLAGS, and then load the second wafer with bond surface facing up, to mate with the top wafer. Note: the second wafer must have alignment marks on the non-bonding surface, in addition to any which may be on the bonding surface. The second wafer would then be moved, with verniers, to align with the electronic crosshair registers, and the bond would now occur with SDB, or the bondchuck would clamp the loadframe/wafer/flag/wafer stack in place, for bonding in the bonder for all other bonding programs.

There are several different tooling sets and bonding programs available, including:

Fusion: typical for Si or SiO2 wafer bonds. Use software program AB1 on the "menu" key, and the either the MTL CMOS-compatible bondchuck, currently labeled with the letter "F", and the matching quartz loadframe/pressure diffuser, marked with green tape, which may be used only immediately after TRL brown-dot RCA or Piranha-HF clean, or equivalent. Two CMOS-compatible bondchucks are currently available, one with a steel vacuum plate, one with teflon. The steel one may prevent bowing more effectively. This is typically done under a vacuum, after a N2 purge, which can help eliminate trapping air bubbles in the bond surface. This bond sequence is usually followed with an anneal, typically Using a TRL diffusion tube which allows MTL brown-dot contamination, in an N2 ambient, usually at 1100C for one hour at temperature. An MTL Au-compatible bondchuck, currently marked with the letter "A", and the quartz loadframe and steel pressure diffuser in the RED tape-labeled box is available for use. The pre-clean requirement for the Au-compatible bond is not as rigorous as with the CMOS, but particles or contaminants will still destroy your work. An RCA clean can be done with Au-labware and the two hot-plates inside the acid-hood, if possible, but at least consider a Using strong wet chemical clean, perhaps in conjunction with a UV-Ozone clean to remove trace organic residues.

Thermocompression: (heat during fusion bonding) This could be used, for instance, to soften an e-beam deposited Au film during bond, in an application of a deposited film being bonded without a CMP. Due to contamination issues, only the Au tooling may be used with heat.

Anodic: for bonding a Si wafer to a pyrex (Na-containing) wafer. Use software program AB1 on the "menu", and the Au-compatible bondchuck, loadframe, and the GRAPHITE pressure diffuser, which will act as a cathode in this process. For the aligner, follow the same sequencing as with the Fusion bonding above, loading the Si wafer first, and the pyrex wafer second.

** In all cases with fusion, thermocompression, or anodic bonding, when installing the bondchuck, make absolutely sure the clamps are in their recesses. If not, they will break the $1500 quartz loadframe when contact is made**

Silicon Direct Bonding (SDB): for bonding multiple MTL CMOS-compatible wafers at the aligner, without having to go into the bonder. Use the teflon SDB tooling and choose the software program SDB, with perhaps a minute contact time. Sequences are similar to fusion, above, except the flags are not inserted, as the separation between wafers is maintained by the aligner. A dial "SDB piston" will induce a bow on the top wafer, ideally presenting an initial contact point, which could radiate outwards. While the SDB dial default value is 1.5, we have found, if the top wafer is rigid, or if the vacuum contact on the top wafer is tenuous, application of this bow force will cause the wafer to pop out of its vacuum seal and drop. The final step at the aligner in SDB is the actual bond contact of the wafers. As this is done with teflon tooling, and without the benefit of a vacuum environment, the wafers may have more bow or trapped air than wafers bonded in the AB1-PV.

Pressure default values: The WEC dial should be set at .5 and ALIGN at 1 to 1.1. Note: both of these are resistive forces opposing the weight of the tool, so a larger pressure means less resulting force down on the wafer. Too much pressure may cause the chuck to "float" out of contact with the wafer. CONTACT force should be set at about 400.

BONDER OVERVIEW:

Wafers bonded with the AB1 program will be clamped onto the bondchuck, and rotated upside-down and placed into the bonder. Make sure the thermocouple aligns with the hole in the bond-chuck, and ALWAYS use a pressure diffuser, of steel, teflon, or graphite, depending on the application, or the quartz loadframe and your wafers, will break. Close the lid and tighten the four clamps with moderate force only, tightening opposing clamps simultaneously.

Chose or create a program appropriate to your needs. A typical FUSION program may include a pump, purge (make sure N2 is flowing on the wall manifold), then re-pump to a lower pressure, sequence. Next, an initial "electrode down" is made where a 5 mm diameter piston applies a small weight to the center of the pressure diffuser, and the flags are removed. Then the second electrode down occurs, where the main, 100 mm dia piston with a heavy contacting force, is applied for a time, then the pumps are turned off and the system is vented.

For THERMOCOMPRESSION (Au-only), variations to the fusion bond include making sure the heat circuit breakers are turned on, and turning them off when done. If heat is being used, never, ever, abort a program, turn off the circuit breakers, or open the chamber while the red light is on, as this would cause significant machine damage. Always set the top and bottom temperature to the same temperature. On cool-down after a high temperature bond, the light will go off at about 250C, and you can open the lid to allow faster cooling only at this point. Remember, CMOS Si-compatible tooling may not be used at elevated temperatures.

For ANODIC bonding (Au-only), attach the conducting strip screwed onto the top of the pressure diffuser, and have the program progress as in fusion with a temperature of 500C. Upon reaching temperature, have your program wait 3 minutes, then apply 800 volts to the top cathode, which will cause Na+ to migrate out of the pyrex, and go into the Si wafer. After some time, often about 5 or 10 minutes, there is a depletion of Na, and the pyrex wafer acts like an insulator, and the current will drop quickly. Have your program call for a final temp of 250C at the end.

PROCEDURE

1. Check Equipment Reservations in CORAL to insure that you reserved the correct machine in the correct facility for the correct date. Another user may have reservations; it is your responsibility to honor them, if this is the case.
2. Use the "Engage" command in CORAL for the equipment that you are about to use; use this command BEFORE you start the operation. Insure that the correct facility is set (TRL) and that your lot name is entered correctly. Enter the number of wafers that you are processing in the comments field.
3. PRELIMINARY CHECKLIST:
   
   Verify that the appropriate accessories for your bond are available. There are separate tools for fusion, SDB, anodic and thermocompression bonding
   Verify that isopropyl and a good supply of fab-wipes for cleaning are nearby.
   Surfaces to be bonded tend to lose their hydrophyllic condition very rapidly, so bring to the bonding area no more than 5 pairs of wafers at a time.
   In the EV-aligner, clean with isopropyl:
   the observable surface of the aligner,
   
   ruler
   
   quartz plate
   
   tray
   
   wafer bond-tools (flags are fragile, check for proper operation)
   
   vacuum wands
   
   surface adjacent to the objectives
   
   interior of the bonder chamber

OPERATION:

Follow screen instructions for aligning.
When in the bonder, make sure the recipe screen is in the forground, then press run.

END:

Put away all tools, loadframes, and pressure diffusers in their containers. The bondchuck can be put back into the aligner or into the tooling box.
Close the bonder Turn off the aligner by pressing the red RESET button and then the green POWER button. "Disengage" in CORAL.