Tube Furnace SOP
Last updated
Last updated
Temperature
generally 1100°C
Diffusion time
generally 30 min for defining source/drain regions
The primary use of the tube furnace is for diffusion of dopant atoms into silicon. The incorpoation of dopant atoms into the Si lattice creates defects in the electronic structure, which are charge carriers, increasing the conductivity of the diffused region and making it either N or P type. Diffusion of a solid into another solid is quite slow, so high temperatures and long times are needed, hence the high-temperature tube furnace.
Our process uses spin on glass containing phosphorus for N doping and boron for P doping.
Tube Furnace (ThermoFisher Manual) with Quartz tube
Quartz rod
Quartz microscope slide, or Fused silica boat
Chip with glass containing phosphorus or boron.
Turn on the furnace.
Press and hold “set/ent” for three seconds until “mode res” is showing. Press the up arrow twice until mode “LCL” is selected. Press “enter” once. Now the furnace will hold the temperature shown. Use the arrow keys to adjust and press “enter” once to set the setpoint.
If the furnace stops and holds at a lower temperature than your setpoint, the high temperature alarm may be too low. Read the instructions on page 6-7 to fix this.
Put the Quartz microscope slide in the entrance of the tube. Do not use a regular borosilicate microscope slide, or it will melt inside the tube. The edge of a fused silica slide is pure white, while borosilicate is a little bit green.
A chip permanently fused to the tube furnace walls when improper slide was used 🔥
Place your chips on the slide.
Put on the heat resistant gloves.
Use the glass rod to push the slide into the center tube, being careful to not scratch the inside of the tube too much
Measure out how far the glass rod needs to be pushed in to place the chips atthe center of the tube furnace.
The rod is extremely hot, and will auto ignite what it touches, or burn through flesh. carefully place it a top the tube furnace
Use the glass rod to push the slide to the other end of the tube.
Wait a few minutes for the slide to cool down.
Use metal tweezers to take the slide out. place it on the upside down beaker to allow it to cool further
Wait 3 minutes before handling the chip.
The furnace is obviously very hot. Keep away from any hot parts of the furnace. The rod will heat up in the few seconds that it is inside the tube, so when removing it, only hold it by the colder end.
The rod and tube also channel heat out of their ends via internal reflection of radiation.
