Metal Lift-Off for Photoresist

This process is typically used in the production of microelectronic devices, such as integrated circuits and other electronic components.

One common method for performing metal liftoff is through the use of S1805 and PMGI bilayer photolithography. A layer of PMGI is applied to the surface of the silicon wafer, followed by a layer of S1805 photoresist. The photoresist layers are then exposed to light using a photolithography process. The sample is developed, which removes the exposed areas and forms a pattern on the silicon sample.

Once the photoresist has been exposed, a layer of metal is deposited on the surface of the sample using a deposition process. The metal layer is then removed using a chemical, which removes the metal from the non-exposed areas of the wafer according to the pattern defined by the photoresist.

TMAH based developer

The remaining photoresist is stripped from the surface of the wafer using a solvent, such as acetone or IPA, followed by stripping the PMGI base layer using a TMAH-based solution. This leaves the metal layer intact in the areas where the photoresist was exposed, creating the desired metal pattern on the wafer.

Here are some examples of TMAH-based developers:

• MF319
• Kemlab TMAH-0.26N

Overall, metal liftoff is an important process in the production of microelectronic devices. The use of S1805 and PMGI bilayer photolithography can provide improved resolution and patterning accuracy compared to other methods. This, in turn, enables the creation of complex and highly integrated electronic circuits and devices.

All samply holders are compatible with the process described below. We recommend using a dedicated holder per process to minimize cross-contamination. The following process describes Metal lift-off for photoresist.

Method

1. Place the silicon samples with S1805/PMGI photoresist into a samply sample holder into a suitable heat-resistant beaker suitable for use on a hotplate.
2. Pour enough acetone into the container to completely cover the samples
3. Place the container on the hotplate and set the temperature to 60°C (140°F).
4. Allow the acetone to heat up until it reaches the desired temperature. This may take several minutes depending on the size and type of hotplate being used.
5. Place a watch glass on top of the beaker and allow the silicon samples to soak in the hot acetone solution for at least 30 minutes. This will help to loosen and remove the S1805 photoresist from the surfaces of the samples.
6. Use a pipette to remove the metal layer on the surface of the sample. If the layer does not fully come off leave the samples in the acetone for a further 30 minutes and repeat.
7. After the samples have soaked in the acetone for the required time. Carefully transfer the samply holder into a beaker of MF319. This will remove the PMGI layer.
8. Allow the samples to soak in the MF319 for at least 10 minutes, or longer if necessary to remove any remaining contaminants or residue.
9. Rinse the samples in Ultrapure water and remove the samples and dry them using compressed air.

Health and Safety

MF319 is a TMAH-based solution and should be handled as per the manufacturer’s instructions.

It’s important to note that this process is only suitable for stripping S1805 and PMGI photoresists from silicon samples. It’s important to use appropriate safety precautions when working with solvents. Wearing gloves, eye protection, and working in a fume hood are examples of this.

Samply sample holders are compatible with a large range of chemicals listed in this compatibility chart. The range of samply sample holders is designed to fit into standard lab beakers (25ml, 50ml, 100ml) eg Fischer.