Stepper 2 (AutoStep 200) Operating Procedures

Work In Progress This article is still under construction. It may contain factual errors. Content is subject to change.

Cleaning the back-side of wafer

If the back side of wafer has some resist residue or particulates, this can cause errors in the interpreted best focus point since the wafer surface may be at a different height.

1. Make sure all work surfaces/spin chucks/hot plates are cleaned! Don’t use wipes, instead use cleaned steel surfaces.
2. Spin coat resist following the recipe for spinning/baking specific resist.
3. Check back-side of wafer thoroughly for resist residue/particulates before loading into system!
4. If you see particulates, try to blow off with high N2 flow first, you may need a razor blade to remove stubborn particles.
5. If you see resist residue, do next:
   1. Place wafer upside down in POLOS spinner using non-contact chuck.
   2. Set spin speed to 2000rpm.
   3. Spin wafer, wait until at top speed.
   4. Squirt Acetone on sample back for 3 seconds. Followed by ISO for 3 sec.
   5. Spin Dry while blowing with N2.
6. Load the wafer on chuck and then stage.

Reticle Loading and Unloading

The alignment of the reticle (mask) to the system is critical for achieving reproducible alignment.  System alignment marks on the reticle are located near the right and left edges of the mask and are 103 mm apart so they do not get exposed within the 100 mm exposure area of the mask.  These marks are put on automatically by Photronix and the gds file can be obtained from Brian Thibeault if you use a different vendor. Use the following procedure to align the mask correctly to the system.

Loading the reticle:

1)   Unlock spindle and swing lamp column to middle position so that the lens is exposed.

2)   Place mask chrome side down so that wording appears correct ( as seen in L-edit file).

3)   Swing lamp column so that objective can be used to align mask, DO NOT tighten spindle lock at this time.

4)   Using your hands and looking through microscope, shift and rotate mask so that the “crosses” are roughly aligned

5)   Tighten spindle lock. This releases a vacuum holder onto the top of the mask so that the mask may be precisely aligned.

6)    Looking through microscope, use alignment knobs (x,y) to translate and rotate(Θ) the mask into position.  First focus the objective by using the knob on top of the microscope.  Use the right alignment mark for the x-axis alignment and both alignment marks for the y-axis and rotation alignments.  NOTE: To get best and fastest results approach alignment from one direction, do not try to wiggle back and forth about the alignment position. Backlash in the mechanics can make this frustrating. You should see equal amounts of light in between all lines when the mask is aligned well (within 0.1 um).

7)   Once mask is aligned, pull the reticle vacuum button to the left of the lens column. The reticle is now vacuumed to the system.

8)   Use the stencil (usually L-shape mask cover), to cover part of the mask plate that you do NOT want to be exposed. If you have just one layer on your mask plate, you do not need to use the stencil. There are also blade apertures that could be used. The knobs on the lamp column  (X,Y) can be adjusted to 100,75,50 and 25% to be open. Fully open blade apertures would be at 100%

9)   You are now ready to proceed with a focus job, map job, or exposure job.

10) This part is important: If alignments are critical, do not just brush through this procedure.  The global alignment requires good, precise alignment of the reticle with the system in order to work correctly.  The local alignment system can adjust for local X and Y misalignment, but not rotational errors.

Unloading the reticle:

1)   Unlock spindle and swing lamp column to middle position so that the lens is exposed.

2)   Once mask is aligned, pull the reticle vacuum button to the left of the lens column. The reticle is now vacuumed to the system