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Wafer Not Present Alarm
Troubleshooting
CLPB |
One item that is often over looked with polish head wafer handling issues is the rotary union. These are made of carbon on ceramic seals and the carbon is the consumable. These parts have a lifetime based on many factors but one is the number of revolutions. The factory warranty is 1 year and they have shown the capability to significantly exceed this lifetime.
ASK BALANCEWORX ABOUT
REPAIR OF YOUR ROTARY UNION |
Rotary Union Testing
Pressurize the inner tube with a good polish head installed for the wafer sensor and lock the chamber. rotate the spindle 360 degrees slowly and see if the chamber vents. this is a good indication that this port has failed.
Based on the version of polish head and pneumatics you have on your CMP tool one robust option is to isolate each chamber of the rotary union. This can be done by clamping a blocking plate to seal off the bottom portion of the spindle. A simple vacuum fixture can be made with a gauge and a manual block valve to attach to each port. of the rotary union.
Pull vacuum on the rotary union and close the manual valve. Now rotate the spindle very slowly 360 degrees and see if the chamber vents or has a significant vacuum loss. repeat for each chamber and if one leaks it is time to send it out for refurbishment. Please feel free to contact us if you need assistance with your rotary union repair.
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Issues during loading
- A good starting point is to check the position of the polish head in the load station. If the problem is in and out the sweep mechanism may have failed from an electrical or mechanical issue. In most cases the rotation should not fail or require adjustment so it is a good idea to check out the homing sensors and verify they are clean and aligned properly. I recommend 242 loctite on the screws to keep them from backing out on the plate that the sensors our mounted on.
- Next, check for good pedestal vacuum with a wafer and it should be set so that without a wafer it does not flicker or change states if water enters the vacuum system.
- Verify the wafer plate is moving up/down at a normal speed. the up should be controlled by pressure and the down by a flow control. One common failure is the 60 psi gauge. You should consider a 0-100 psi gauge which we find to be a better long term solution. The failure of the internal seals can also prevent the wafer from coming all the way to the up position. This can be checked by pulling up on the plate and checking for additional movement.
- Next, verify that the entire assembly is moving up with pressure and is controlled down with the flowcontrol. Check the main air cylinder and airlines for leaks. Also, while the cup is in the up position, there should be minimal up-play. This can be caused by cylinder bolts that are loose, or the coupler is failing. This position is critical to center the wafer.
- Check the centering mechanism. The first step is to verify that the N2 purge is toggling correctly and set at the correct pressure. Check the valve that changes from vacuum to water and also from vacuum to N2 purge for failure. the DI water is pressurized so make sure to test appropriately. A good test is to place a wafer on the wafer plate and repeat with vacuum again using one of the centering mechanisms. Load the wafer on the head. Repeat for each by putting the wafer against each one of the centering mechanism. Make sure to repeat several times. This will help you identify failed or binding parts or pressure issues during wafer load.
- Inspect the polish head pneumatics for loose connections or broken wires. A previous broken wafer could damage a valve if filters are not installed or if installed and not cleaned properly. Many of the new tools have swagelock type screens on the membrane lines. If you haven't checked these, this could be causing vacuum issues if they are not adequately cleaned following a wafer breakage event. Contact us if you would like to implement a filtering solution on your membrane lines.
- Check vacuum levels for the membrane, but be careful, volume is critical! An inexpensive solution is to use a rotometer and establish a baseline by pulling the vacuum on the output side.
- Inspect the polish head for any tears or related issues. Unless something is obvious, this is usually the last step. the consumables are expensive and for cost concerns should be replaced as a last resort. Membrane carriers that are made from materials that are sticky to the touch can also cause problems. The issue is that the membrane can stick to certain wafer sensors and cause false detection of the wafer not being loaded properly. Contact us if you would like more information on an inexpensive solution to this problem.
- Many other failure modes and testing procedures are used in the industry, this guide should help you narrow down the area and allow you to continue to dig further for the root cause. Sometimes complex problems have simple cost effective solutions!
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