3612 is a G/I line positive resist that is the lab standard for films of 1µm and 1.6 µm.

For whole 4” wafers (silicon, glass and quartz)

Singe/ Prime Before applying resist the wafers must be singed in order to drive off any moisture on the surface of the wafers.  Wafers that have just come out of a furnace operation may not have to go through a singe step.  Prime refers to the use of HMDS as an adhesion promoter to help the resist stick to the wafer surface.  There are two ways to do the Singe/Prime step:

1. Use the Yield Enhancement Systems (YES) oven.  The YES oven has a standard program that takes about 30 minutes to complete.  At the end of the program an alarm will sound to alert you that the singe/prime is done.  Only Teflon cassettes dedicated to the YES oven (two brown dots) are to be used in the system.
2. Use a combination of 150°C singe oven and the Prime Station on the SVG coater.  The 150°C singe oven is located right of the BlueM oven and is pre-set for 150°C.  Use a Teflon litho cassette for the 30 min bake.  At the end of the bake remove the wafers (careful- they are hot) and transfer them into a metal cassette for the SVG coat prime operation.  Be sure that the prime station is set on Prog 1.

Coat The Silicon Valley Group (SVG) resist coat system has two tracks.  Either one may be used, just be sure that you have programmed and enabled the correct track.  There are three parts to the system and you need to verify that the desired programs are put in. The three parts to the system are:

1. VacPrime station.  This station applies HMDS to the wafer while it rests on a hot plate, 125°C.  Do not consider this an alternative to the singe step.  To prime wafers use Prog 1. 
   If you have used the YES oven do not use the prime station.  Prog 9 (End) will by-pass the station.
2. Coat station.  This is where the resist is applied to the wafers.  The thickness of the film is controlled by spin speed and time.  For 1.0µm films use Prog 7 and for 1.6µm films use Prog 8.
3. Prebake station. The function of a prebake is to drive off the solvents on the resist.  The thicker films require a bit more time on the prebake hot plate. For 1.0µm resist use Prog 1 and for 1.6µm resist use Prog 2.

Here is a little chart for handy reference

One final note about prebaking; if you cannot use the prebake hot plate, for example, you are processing both sides of the wafer, you may use the 90°C oven or other hot plates. For 1.0µm resist either use one minute on a 90°C hot plate or 25 minutes in the 90°C oven. You will find a preset hot plate at 90°C across from the KarlSuss aligners.

Exposure Chart   Please refers to the chart on our web site or to exposure charts next to each aligner. Some labmembers find looking at the logs for each machine helpful in determining the correct exposure time for their work.

Post Exposure Bake  After exposing the wafer you may want to do a post exposure bake.  The purpose of this bake is to drive off more of the remaining solvents.   It is required to resolve features 2µm or less.  A 115°C hot plate is located across from the Karlsuss aligners and is left at temperature. 

                                     For 1.0 µm thickness, 60 seconds on 115 °C hot plate

                                     For 1.6 µm thickness, 90 seconds on 115 °C hot plate

Develop After exposure or after exposure and post exposure bake the patterns are developed using the SVG develop track system.  It looks a lot like the SVG coat system, except that there are only two stations instead of three.  They are:

1. Develop station. This station applies the developer (LDD26W for 3612 resist) for a pre-programmed amount of time and ten rinses the developer off using DI water. For 1.0µm thick resist use Prog 3 and for the 1.6µm use Prog 4.
2. Postbake.  This is the final bake of the resist.  It completes the cross-linking of the polymers and makes the resist strong enough for additional processing, such as wet or dry etching.  Thicker resist films need longer bake times.  For 1.0µm thick resist use Prog 1 and for the 1.6µm use Prog 2.

Here’s another handy table:

For pieces and smaller wafer sizes

The steps for patterning a wafer using photolithography on smaller wafers or pieces of wafers are the same as outlined above.  The major difference is that you cannot use the automated equipment.  Here is a description of the process flow using the lab’s manual equipment.

Singe/ Prime.  Use the YES oven.  There are dedicated Teflon cassettes for 3 inch wafers.  For smaller wafers or pieces, use the Teflon tray that is provided.

Coat.  Use the Headway or Laurell to manually dispense the resist.  You will need to bring the resist over to the spinner in an appropriate container.  You will also need to provide and program (for the laurel) the spin speed and time to achieve the desired resist thickness.

Prebake.  You have two choices on how to prebake the samples:

1. The hot plate across from Karlsuss aligners is set to 90 °C.  One minute for 1.0µm thick resist is recommended.
2. The 90 °C oven is located left of the BlueM oven.  A bake of 25 minutes is recommended for a resist film of 1.0µm.

Exposure Chart.   Please refers to the chart on our web site or to exposure charts next to each aligner. Some labmembers find looking at the logs for each machine helpful in determining the correct exposure time for their work. (Insert the Exposure chart)

Post Exposure Bake.  After exposing the wafer you may want to do a post exposure bake.  The purpose of this bake is to drive off more of the remaining solvents.   It is required to resolve features 2µm or less.  A 115°C hot plate is located across from the Karlsuss aligners and is left at temp. Please don’t temper with the knob!

                                     For 1.0 µm thickness, 60 seconds on 115 °C hot plate

                                     For 1.6 µm thickness, 90 seconds on 115 °C hot plate

Develop.  You’ll need to use a beaker filled with developer (LDD26W) to perform an immersion develop.  After the develop rinse the samples in DI water and blow dry.  This work is done at the wetbench located near the pre and post bake ovens.  The recommended procedure is to develop the sample for 30 secs, rinse and dry.  Inspect the development under the microscope to determine whether more developing is needed.  Do not postbake as it will stop any further development.

Postbake.  Again, there are two choices for postbaking the samples:

1. The two hot plates across from the Karlsuss aligners or the two hot plates located right of the Headway can be set to 110°C.  One minute for 1.0µm thick resist is recommended.
2. The 110°C oven is located left of the BlueM oven.  A bake of 25 minutes is recommended for a resist film of 1.0µm.

3612 Process Flow (terse version)

These process flow steps are provided for easy reference and should not be used in place of training or reading the above material.

1.0µm

1. Singe/Prime  use pre-programmed YES oven. Or use singe oven for 30 minutes at 150°C and the prime station of the SVG coater, Prog 1.
2. Spin  svgcoat spin Prog 7 (spin 5.5K RPM, 30 seconds).
3. Prebake svgcoat bake Prog 1 ( 90°C for 1 minute).
4. Expose check exposure charts or aligner logs.
5. Optional: Post Exposure Bake at 115°C for 1 minute (skip this step for >2µm resolution). Doing this also improves the adhesion during wet etch (6:1 Buffered HF).
6. Develop svgdev Prog3 (60 seconds in LDD26W)
7. Postbake svgdev bake Prog 1  (110°C for 1 minute)

1.6µm

1.      Singe/Prime  use pre-programmed YES oven. Or use singe oven for 30 minutes at 150°C and the prime station of the SVG coater, Prog 1.

2. Spin svgcoat spin Prog 8 (spin 2 KRPM, 30 seconds).
3. Prebake svgcoat bake Prog 2 ( 90°C for 2 minutes).
4. Expose check exposure charts or aligner logs.
5. Optional: Post Exposure Bake at 115°C for 1 minute (skip this step for >2 µm resolution). Doing this also improves the adhesion during wet etch (6:1 Buffered HF).
6. Develop svgdev Prog 4 (120 seconds in LDD26W)

7.      Postbake svgdev bake Prog 2  (110°C for 2 minutes)