Haico Kok | ASML: How do stitching errors in lithography affect the contrast and image quality of AR displays?
34:33 - 36:32
Other snippets from this talk
Summary of the clip:
How do stitching errors in lithography affect the contrast and image quality of AR displays?
A stitching error divided by the grating pitch produces phase shifting, so the waveguide combiner has to be circular. Simulations modeled a typical waveguide layout and pupil size of 2.2 nanometer. The modulation transfer function shows angular frequency and contrast. Blue is the ideal image without aberration; red adds the impact of a stitching area perpendicular at 10, 20, 50 and 100 nanometer stitching errors.
Many field points on the waveguide were simulated because some hit the stitching area smashing the center of the pupil, while others hit along the edge, so results vary. That is why large line variation appears. Human vision resolution is also plotted; it is not one number and varies from person to person, but roughly as shown. At 50 nanometer overlay, today’s AR display resolution gives an impact comparable to human vision.
If you go lower than 50 nanometer, the impact becomes much smaller, and at the actual scanner performance it is hardly visible. It does not scale linearly; it scales quadratically. From one value to another is not a factor of two but a factor of four in contrast impact. At 100 nanometer it is not okay: at high resolutions in your image, you completely lose your contrast.
In this short video, you can learn:
* Stitching error divided by grating pitch sets the phase shifting in a circular waveguide combiner.
* At 50 nanometer overlay, the modulation transfer function contrast impact is comparable to human vision at today’s AR display resolution.
* The contrast penalty scales quadratically, so 100 nanometer overlay can completely erase high-resolution contrast.
📋 **Clip Abstract** This clip models how lithographic stitching errors create phase shifting in waveguide combiners and degrade modulation transfer function contrast. It shows that 50 nanometer overlay is comparable to human vision at current AR display resolution, while 100 nanometer is unacceptable and scaling is quadratic, not linear.
About the speaker:
* Speaker: Haico Kok
* Company: ASML
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#StitchingError, #ModulationTransferFunction, #WaveguideCombiner, #ContrastLoss, #ARDisplays, #Lithography
This is a highlight of the presentation:
A Lithographer’s Perspective on Manufacturing Waveguide Combiners for AR Glasses
More Highlights from the same talk.
06:19 - 08:06
How fast can automated semiconductor lithography clusters pattern AR waveguide wafers?
How fast can automated semiconductor lithography clusters pattern AR waveguide wafers?
Litho is always used in combination with etch; the basic flow starts by spin-coating a wafer with photoresist. Exposure happens in the litho tool, while spin-coating occurs in a connected track. The resist is then developed, much like old-fashioned photography, leaving a patterned resist. That pattern is typically transferred into the material. In this case, it can be etched directly into glass or silicon carbide, either with a straight etch or a slanted etch to produce slanted gratings.
The track is always connected to the litho tool, together called a litho cluster. A bare wafer enters the track, moves through coating and litho develop, and simply comes out patterned. There are no manual steps in between; the process is fully automated. Throughput depends on the tool type, ranging between 200 wafers per hour and the highest system at over 400 wafers per hour.
At the fastest throughput, over 400 wafers per hour means a fully patterned wafer emerges every eight seconds. That cadence matters because the litho cluster output sets the pace before etching and later design choices. The next design parameter is grating pitch, moving from process flow into design. Automated cluster throughput and grating geometry together shape what can be manufactured.
In this short video, you can learn:
* Litho is always paired with etch, starting from spin-coated photoresist and ending with a pattern transferred into glass or silicon carbide.
* The track is permanently connected to the litho tool as a litho cluster, so bare wafers enter and fully patterned wafers exit with no manual steps.
* Throughput ranges from 200 to over 400 wafers per hour, with 400 wafers per hour equating to a fully patterned wafer every eight seconds.
📋 **Clip Abstract** The clip explains the basic litho process flow for patterning wafers, combining spin-coating, exposure, develop, and etch, including straight or slanted etches for slanted gratings. It then describes the automated litho cluster and its throughput, from 200 to over 400 wafers per hour, or one fully patterned wafer every eight seconds, before turning to grating pitch.
About the speaker:
* Speaker: Haico Kok
* Company: ASML
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#PhotoresistPatterning, #SlantedGratingEtch, #SiliconCarbideEtch, #LithoClusterThroughput, #ARWaveguides, #SemiconductorLithography
16:33 - 18:19
Why is silicon carbide highly attractive for AR waveguides, and what grating pitch does it require?
Why is silicon carbide highly attractive for AR waveguides, and what grating pitch does it require?
Silicon carbide is the high-refractive-index candidate everybody is talking about for AR waveguides, and it brings several benefits. One benefit is less often mentioned: it allows air gapless designs, which matters if you want lightweight, simple waveguides. The trade-off is that you lose the benefit of large field of view, but you get a very simple stack with two lenses, front and top. That combination makes silicon carbide very attractive.
You can calculate the required grating pitch by plugging in the refractive index of silicon carbide, which is 2.6. That gives 309 nanometers. The comparison between a green waveguide and a full-color waveguide is on the slide. Their pitches are not that different, because green's wavelength happens to sit between red and blue. So supporting full color does not make as much difference as one might expect. If you buy a tool, it is not cheap; you want it usable for some time.
For exit pupil expansion, the most basic architecture of such a waveguide always has three gratings: in and outcoupling, and then a turn grating. Its goal is to provide a bigger eye box and a uniform one, if possible. This is the architecture being discussed alongside silicon carbide's refractive index and the 309-nanometer grating pitch.
In this short video, you can learn:
* Silicon carbide's 2.6 refractive index gives a required grating pitch of 309 nanometers.
* Silicon carbide enables air gapless designs for lightweight, simple waveguides, but it trades away large field of view for a simple stack with two lenses.
* Green and full-color waveguide pitches are not that different because green's wavelength lies between red and blue, and the basic architecture uses three gratings, with a turn grating for a bigger, uniform eye box.
📋 **Clip Abstract** Silicon carbide is attractive for AR waveguides because its high refractive index enables air gapless, lightweight designs, albeit without large field of view. With an index of 2.6, the required grating pitch is 309 nanometers, and green versus full-color pitches differ little; exit pupil expansion relies on three gratings, including a turn grating for a bigger, uniform eye box.
About the speaker:
* Speaker: Haico Kok
* Company: ASML
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#SiliconCarbide, #GratingPitch, #AirGaplessDesign, #ExitPupilExpansion, #ARWaveguides, #AugmentedReality
12:45 - 14:42
How do you calculate the exact grating pitch required for an AR waveguide?
How do you calculate the exact grating pitch required for an AR waveguide?
The light engine sits over there, the eye here, and the beam hits the middle of the field of view roughly perpendicular to the incoupling grating. The grating diffracts it by the diffraction angle, so the grating equation gives that angle. The diffraction angle has room to play with, but it must sit between two boundaries: total internal reflection and a practical maximum.
Many in the literature take the maximum angle as 90 degrees, which makes it nonsensical: that light would just continue, never hit the outcoupling grating, or the exit pupils would be so far apart that imaging gets very nasty. So a maximum angle is included, set at 70 degrees. The total internal reflection condition is one over the refractive index; averaging the two angles gives the basic pitch equation.
If you plug in green for a green waveguide, with a high refractive index glass of index two, and put the angle at 70, the result is 370 nanometer grating pitch. Lovely. The basic pitch equation only contains the wavelength, the field of view the eyepiece is supposed to handle, and the refractive index of the material. The calculation starts from the grating equation, constrains the diffraction angle, then averages the two boundaries.
In this short video, you can learn:
* The diffraction angle must lie between the total internal reflection angle and a practical maximum, set at 70 degrees.
* Taking 90 degrees as the maximum is nonsensical because light never hits the outcoupling grating or exit pupils become too far apart.
* For green in high-index glass with index two and a 70-degree angle, the grating pitch is 370 nanometers.
📋 **Clip Abstract** A grating equation sets the diffraction angle for an incoupling grating, bounded by total internal reflection and a practical maximum of 70 degrees. Averaging those limits yields a basic pitch equation; for green light in index-two glass it gives a 370 nanometer grating pitch.
About the speaker:
* Speaker: Haico Kok
* Company: ASML
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#GratingPitch, #IncouplingGrating, #TotalInternalReflection, #GratingPitch370nm, #ARWaveguides, #DiffractiveOptics