Metricon Prism Coupler
The Metricon Prism Coupler allows for wafer measurements without an initial knowledge of the thickness. It allows for high accuracy measurements of many materials and substrates. The threshold for thickness on this device is 3000 Å to 4800 Å so it is mainly used for thick film measurement. This unit also allows for dual film measurements, localization of modes in waveguides and index of refraction measurements for bulk and substrate materials.
633nm He-NE laser
Measurement time is 1-25 seconds with standard table and 15-75 seconds with high resolution table
|Film Type/Index||Thickness and index measurement||Thickness only (assume index)|
|Silicon dioxide (n=l.46) over Si||0.48-150 microns||0.20-0.48 microns|
|Photoresist (n=l.63) over Si||0.42-150 microns||0.18-0.42 microns|
|Photoresist (n=l.63) over Silicon dioxide*||0.70-150 microns||0.30-0.70 microns|
|Polyimide (n=l.72) over Si||0.38-150 microns||0.15-0.38 microns|
|Polyimide (n=l.72) over Silicon dioxide*||0.50-150 microns||0.16-0.50 microns|
|Si oxynitride (n=l.80) over Si||0.35-150 microns||0.14-0.35 microns|
|Si oxynitride (n=l.80) over Silicon dioxide*||0.45-150 microns||0.13-0.45 microns|
|Si nitride (n=2.0) over Si||0.32-150 microns||0.12-0.32 microns|
|Si nitride (n=2.0) over Silicon dioxide*||0.30-150 microns||0.15-0.30 microns|
*High-index films over substrates or underlying films of lower index other than silicon dioxide are sometimes measurable at thicknesses up to half as thin as the above limits. Optional shorter wavelengths are also available to extend the measuring range to thinner films. Please consult Metricon for details.
Turn the key on the back of the big cream colored box to use the 633nm laser. If you want to use the 1550nm laser, flip the switch on the black box behind the monitor. Flip the power switch on the back of the small cream colored box to the right of the monitor. If the computer isn't on turn it on. Double click on the Metricon icon on the desktop. Check to make sure the laser hits the prism in the top right corner. If it doesn't hit there, adjust the position of the laser using the two knobs on the front of the prism box.(This has been done and shouldn't need to be adjusted) See pictures
Find out the index of refraction for the sample to be measured. Make sure that the prism in the box is the right one. If not look under the table for a bag with the prisms in it and replace the prism very carefully. Changing the Prism Loosen the screw above the sticker on the prism. When it is loose twist it out about 45 degrees and lift it out. Put it in the bag and put the new prism in the box carefully. If you want to know the index of refraction at a certain wavelength, use the 1550nm laser otherwise use the 633nm laser. On the screen that appears after loading the program, check the code for the prism and make sure it is correct fot the prism installed. The code is located above the prism. Click on TE. TE modes are mainly used but sometimes it can be used in the TM mode (for the 1550nm laser). To switch to the TM mode check the TM box on the screen and open up the prism box. In the bottom right of the box there is a cable connected to a metal piece with two wheels. Spin the wheel closest to the front of the box to 45 degrees. This should put it in the TM mode. Check the substrate index on the top right of the screen. If you are going to use silicon make sure it is 3.4. If it is another material, enter in that index of refraction. Enter the wavelength of the laser to be used. Click OK Hit Auto Ref and wait for awhile. It will run some tests and after it is done two sharp peaks should appear on the screen. After the Auto Ref has finished, adjust the gain on the small box to be between .8 and 1. Click OK Wafer Placement Remove the lid and hold the wafer next to the prism with the side to be measured facing the prism. Flip the switch on the side of the prism box. A metal rod will push on the back of the wafer so it it is pressed tightly against the prism. Make sure that the lid doesn't hit the wafer if the lid is put back on.
Click on measure. It will find the modes. If only one mode appears (a valley on the screen) adjust the pressure on the right side of the big box and/or move the wafer so it measures a different spot. If the peaks are too shallow or too deep adjust the pressure. If the peaks are too small more pressure is needed and if the peaks are too big less pressure is needed. NOTE: The peaks should fit nicely on the graph on the screen. If there are erroneous peaks that are obviously different that the others you can remove them after it has finished measuring. Simply click on the redline at the peak. It will display the index of refraction and the thickness with the standard deviation. When finished make sure to turn off the lasers and the power on the small box. Exit the program as well.