Heidelberg µPG 501

Heidelberg µPG 501

Essentials
Full name	Heidelberg µPG 501
Manufacturer	Heidelberg Instruments
Description	Table-top maskless aligner
Location	Cleanroom 2
Manual	Digital copies on instrument PC desktop
Responsibility
Primary	Nader
Secondary	Martin

The Heidelberg μPG 501 is a tabletop maskless (i.e. direct-write) ultra-violet photolithography system. It utilizes a 10 W light emitting diode operating at 390 nm, a 600×800 pixel digital micromirror device, and motorized stage to expose patterns on resist-coated substrates. The system has a writing speed of 50 mm²/min for the resist AZ 1505 on silicon with a resolution limit of 1 µm, and is therefore well suited for rapid prototyping, as well as for writing large structures that are otherwise too time consuming for EBL. The Heidelberg is compatible with DXF, GDSII, and CIF CAD files. The main instrument PC is offline, but it's connected on an online design PC. The two share a screen, mouse, and keyboard, but you can switch between the two PCs by pressing ctrl, ctrl, enter.

Specifications

• LED emission wavelength: 390 nm
• LED power: 10 W
• Exposure range: 4 ms to 90 s
• Maximum substrate size: 6 × 6 inches² (152.5 × 152.5 mm²)
• Minimum substrate size: 6 × 6 mm²
• Maximum writing area: 125 × 125 mm²
• Substrate thickness: 0 to 6 mm
• Substrates with thickness variations of below ± 20 µm are recommended

Operating instructions

Video on how to operate the Heidelberg μPG 501:

Click here to watch the video on YouTube

Measure the diode intensity

1. Make sure the stage is empty.
2. From the 'µPG 501 menu', select 'Tools', and then 'Intens. diode'.
3. Follow the on-screen instructions. The intensity of the diode will be measured at 40°C. Enter the measured value into the logbook on the design PC.

Load your chip

1. Press 'Load substrate' in the software menu. The stage will be moved into the loading position, and a software dialog box will open.
2. Open the dust cover.
3. Place your chip or substrate on the center of the stage, over the four small vacuum holes. Please note the orientation of the coordinate system; the x direction points outwards from the front of the instrument.
4. Enable the vacuum, by toggling the vacuum switch. Make sure your sample is firmly fixed in place. For larger substrates (e.g. 2 inch wafers or larger), you may need to enable suction on additional vacuum regions. Talk to a cleanroom staff member if that is the case.
5. Close the dust cover.
6. Press OK in the software dialog box. The stage will be moved to it's home position, and another dialog box will open.
7. Make sure that the substrate is below the writehead (metallic disc with red light emanating from the center). Not doing so may cause the writehead to be driven into the sample during the next step, potentially severely damaging the system.
8. Press 'yes' in the dialog box for pneumatic focusing (recommended, but requires a distance of approx. 3 mm to the edge of the sample), or 'no' for optical focusing (use for small samples, or when writing close the sample edges).

Design conversion

1. Copy your design file to the design PC.
2. On the instrument PC, copy to the design file to the correct path depending on the design format (e.g. C:\HIMT\designs\dxf, etc).
3. Select 'Start Conversion Interface' in the 'µPG 501 menu'
4. Create a new job file, by selecting 'File' and 'New' in the conversion interface. Use job file name along the lines of NAME_DATE.
5. Work through the conversion interface. If you plan on performing an alignment exposure, remember to uncheck 'Automatic Centering', and press the 'Reset' button.
6. Finish converting your design by clicking 'Complete Tasks' and then 'Complete Expose Jobs'.

Exposure

1. Click 'Select Design' in the 'µPG 501 menu', and select your converted file (e.g. C:\HIMT\LICSource\<<Your job name>>\expose.cfg).
2. In the right panel of the 'µPG 501 menu', under 'Exposure mode', select the type of exposure you want.
   1. 'Standard Exposure': For blank chips
   2. 'Alignment': For aligning exposures to e.g. chip edges, crosses, etc.
   3. 'Target Mode': Allows users to draw squares to be exposed.
3. Press 'Next'
4. Set your exposure time and defocus (e.g. obtained from a dose test). For an alignment exposure, locate the features (e.g. crosses) that you wish to align to, and enter their corresponding design coordinates.
5. Start the exposure. A progress bar will be shown along with the time remaining.
6. Fill out the log book.

Preparing a dose test

The 'µPG 501 menu' software makes it easy to perform a dose test for a given combination of e.g. resist, substrate, developer, bake-out time and temperature. Two parameters can be varied; the exposure time and the defocusing. If you vary both of them, you'll end up with a two-dimensional grid pattern, where the exposure time increases from top to bottom, and the defocusing increases from left to right. Depending on your design pattern, consider inserting a dummy structure to help you identify the orientation of your dose test later on.

1. Start by selecting the design pattern (press 'Select Design' in the menu).
2. Then select 'Control Panel' from the 'Tool' menu. This brings up a separate window with the title 'Panel'.
3. Select the 'Series' tab.
4. Enter your desired dose test parameters, and the step size of the dose test grid. The step size must be larger than your pattern dimensions.
5. Press 'Start Exposure Series'.
6. After developing your dose test, find the best combination of exposure time and defocusing for your particular design pattern.

Improving the overlay accuracy

The Heidelberg's stage is not calibrated to an absolute length (e.g. NIST) scale. As a result, when performing overlay exposures over patterns written with other instruments, such as the Elionix, the design pattern must be scaled in both the x and y dimensions for the length scales to match. This can be easily done in the conversion interface. For some use cases, this will yield an acceptable overlay accuracy, but for more demanding scenarios, further corrections must be made.

The stage's x and y axes are not perfectly orthogonal to each other, but rather the angle between the two is approx. 89.996°. This leads to a skewing of the written pattern, and the larger its size, the greater the overlay error becomes. This problem can be circumvented by 'pre-distorting' the design file, so that when written, it will yield the intended design. This can be done using the following steps:

1. Open your design in CleWin.
2. Make sure the full design is in a single hierarchical cell (i.e. is flat). If not, flatten it.
3. Save it as a DXF file.
4. Open the program 'Coordinate Adjustment' on the desktop of the design PC.
5. Open your newly created DXF file.
6. Select a name for the converted file.
7. Start the conversion. The pattern will be 'pre-distorted' using the measured parameters shown below. These need to be periodically measured.
8. Perform an overlay exposure as per usual, using the pre-distorted file. However, the coordinates of your reference structures (e.g. crosses) should be the ones from your original design file.

Troubleshooting

Alignment doesn't work?

Perhaps the configuration file randomly disappeared. Follow the guide on the desktop in order to restore it.

Remote access

• TeamViewer: uPG_501
• LogMeIn: HEIDELBERG TRANSFER (CR2)