LithoForge

DIY semiconductor lithography toolkit for MSLA printers.

Process calculators, mask designer, OPC engine, and spacer lithography tools built for hobbyists using consumer LCD/MSLA printers (Elegoo Mars 5 Ultra and compatible).

Validated against the 2025 Wiley maskless LCD lithography paper and Sam Zeloof's home chip fab.

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What it does

Module	Purpose
lithoforge.Mask	Draw mask patterns in micrometers, export PNG for your MSLA printer
lithoforge.opc	Rule-based Optical Proximity Correction for 405 nm exposure
lithoforge.process	Spin thickness, exposure time, develop, etch, and oxide calculators
lithoforge.spacer	SADP spacer lithography -- calculate 50-200 nm features from micron mandrels
lithoforge.structures	Pre-built MOSFET, DRAM cell, Van der Pauw, Hall bar, and test structures
lithoforge CLI	All calculators from the terminal

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Hardware this targets

Parameter	Value
Printer	Elegoo Mars 5 Ultra (or any 405 nm MSLA)
LCD pixel pitch	18 x 18 um
Native resolution (contact mode)	~18 um
With 20x objective (NA 0.40)	~0.9 um
With spacer lithography	50-200 nm
Photoresist	AZ 1512 (recommended), S1813, or dry film

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Install

pip install lithoforge

Or from source:

git clone https://github.com/OutBlade/lithoforge
cd lithoforge
pip install -e .

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Quick start

Python API

from lithoforge import Mask
from lithoforge.process import spin_thickness, exposure_time

# Design a mask
mask = Mask(500, 300)           # 500 x 300 um field
mask.rect(100, 100, 10, 50)    # 10 x 50 um rectangle
mask.alignment_mark(20, 20)    # crosshair alignment mark
mask.cd_bars(20, 200)          # critical dimension test bars
mask.save("layer1.png")        # ready for your slicer

# Calculate process parameters
t = spin_thickness("AZ1512", 4000)
print(f"Thickness: {t['thickness_nm']:.0f} nm")

e = exposure_time("AZ1512", intensity_mW_cm2=3.0)
print(f"Expose for: {e['exposure_time_s']} s")

CLI

# Resist thickness from spin speed
lithoforge thickness AZ1512 4000

# Exposure time (3 mW/cm2 intensity)
lithoforge expose AZ1512 3.0

# Wet etch calculator
lithoforge etch BHF_7_1 100

# Resolution limit for 20x objective
lithoforge resolution --magnification 20 --na 0.40

# Spacer lithography: 2 um mandrel -> 100 nm spacers
lithoforge spacer 2000 4000 110 --card

# Thermal oxide (Deal-Grove model)
lithoforge oxide 1100 60

# List all supported resists or etchants
lithoforge resists
lithoforge etchants

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Mask design

from lithoforge import Mask

m = Mask(width_um=1000, height_um=600)

# Primitives
m.rect(x, y, w, h)                     # rectangle
m.circle(cx, cy, radius)               # filled circle
m.ring(cx, cy, r_outer, r_inner)       # annular ring
m.polygon([(x0,y0), (x1,y1), ...])    # arbitrary polygon
m.line(x0, y0, x1, y1, width_um)      # line with width

# Alignment and metrology
m.alignment_mark(cx, cy, size_um=60)   # crosshair + box
m.vernier(cx, cy, pitch_um=10)         # vernier scale for overlay measurement
m.cd_bars(x, y)                        # critical dimension test bars

# Boolean operations
m.invert()                             # swap exposed / unexposed
m.merge(other_mask, "union")           # union / intersect / subtract

# Export
m.save("mask.png")                     # standard PNG
m.save_for_mars5("mask.png")          # PNG with correct DPI metadata
m.preview()                            # matplotlib preview window

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Optical Proximity Correction

from lithoforge import Mask
from lithoforge.opc import apply_opc, simulate_aerial_image

mask = Mask(200, 100)
mask.rect(10, 10, 5, 80)

# Apply OPC corrections
corrected = apply_opc(
    mask.get_array(),
    pixel_pitch_um=18.0,
    wavelength_nm=405.0,
    na=0.40,              # NA of your objective
    bias_nm=50,           # grow features by 50 nm to compensate shrinkage
    corner_serif=True,    # add serifs to convex corners
    line_end_extension=True,
)

# Simulate what the aerial image looks like
aerial = simulate_aerial_image(corrected, na=0.40, defocus_um=1.0)

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Spacer lithography (50-200 nm)

from lithoforge.spacer import calculate_spacer, spacer_process_summary

# 2 um mandrel, 110 nm Ni film -> ~100 nm spacers
result = calculate_spacer(
    mandrel_width_nm=2000,
    mandrel_pitch_nm=4000,
    film_thickness_nm=110,
)
print(result)

# Print a full process card
print(spacer_process_summary(2000, 4000, 110))

Spacer lithography process (minimal equipment ~$450):

1. Print mandrel mask on AZ1512 with Mars 5 Ultra + 20x objective
2. Electroless Ni-P plate for ~7 min at room temperature
3. Etch back with oxygen plasma (or timed 10% HNO3)
4. Strip resist mandrel in acetone
5. Result: ~100 nm Ni lines at 2 um pitch

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Pre-built structures

from lithoforge import Mask, structures

m = Mask(500, 500)

# NMOS transistor (4-layer process)
structures.nmos_active(m, cx=250, cy=250, gate_length_um=2.0, gate_width_um=20.0)

# DRAM cell array -- same as Dr. Semiconductor's 2026 demo
structures.dram_array(m, origin_x=50, origin_y=50, rows=4, cols=5, layer="active")

# Test structures
structures.van_der_pauw(m, cx=100, cy=100)    # sheet resistance
structures.hall_bar(m, cx=300, cy=100)         # carrier mobility
structures.serpentine_resistor(m, x=50, y=300)
structures.resolution_target(m, cx=400, cy=400)

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Process database

Resists

Name	Type	Sensitivity	Notes
AZ1512	Positive	55 mJ/cm2	Best for 405 nm MSLA
S1813	Positive	150 mJ/cm2	Very well documented
AZ5214E	Image reversal	40 mJ/cm2	Lift-off and negative tone
DRY_FILM_PCB	Negative	30 mJ/cm2	No spin coater needed

Etchants

Name	Target	Rate
BHF_7_1	SiO2	100 nm/min
KOH_30PCT_80C	Si (anisotropic)	1000 nm/min
TMAH_25PCT_80C	Si (anisotropic)	600 nm/min
AL_ETCHANT_A	Al metal	30 nm/min
DILUTE_HNO3_10PCT	Ni (spacer etchback)	50 nm/min

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Examples

File	Description
examples/01_first_mask.py	First exposure test -- contact mode
examples/02_mosfet_mask_set.py	3-layer NMOS process
examples/03_spacer_lithography.py	SADP to 100 nm features
examples/04_dram_cell_array.py	5x4 DRAM array (Dr. Semiconductor style)

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Safety

Working with photoresist chemicals and etchants requires proper precautions. LithoForge prints hazard warnings for every etchant. Key rules:

• HF and BHF: full face shield, neoprene gloves, calcium gluconate gel nearby
• KOH / TMAH: chemical splash goggles, gloves, fume hood
• Photoresist solvents: flammable -- no ignition sources
• Start with dry film resist and washing soda developer (both very safe) before progressing to liquid resist and acid etchants

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References

• Low-Cost Maskless Photolithography Using LCD 3D Printer (Wiley 2025)
• Sam Zeloof Home Chip Lab
• Dr. Semiconductor DRAM in a Shed (Hackaday 2026)
• AZ1512 Process SOP -- University of Washington

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License

MIT