Opti

Fly

To tackle uneven and other types of non-flat substrates a robust precise, and high-speed autofocus system is necessary: Meet OptiFly technology for laser beam lithography.

Introduction

OptiFly technology overcomes substrate imperfections during lithography by maintaining constant focus. Its high-speed autofocus system enables the objective lens to keep focus on challenging substrates even at high scan speeds, ensuring precise exposure despite uneven coatings and warpage

Precision, Speed, and Adaptability

Key features

With an optical detection limit of 10 nm of height variation, our autofocus (AF) system ensures that the focus is captured to a high level of precision. This allows for accurate automatic alignment of the UV laser spot to the substrate.

With a high-speed measurement system we can track the substrate height variations in real-time. The distance between different measurement positions along the scan axis are dependent on the scan speed, and can vary from a few microns to sub-micron. This distance range can account for typical coating and substrate height variations

The closed-loop controlled encoded actuation of the lens with a high resolution allows the lens position to be tracked and precisely controlled. To take advantage of this capability, a height map of the exposure area is captured before each job. If the optical autofocus signal is lost for any reason during exposure, the system reverts back to the initial height map and uses the interpolated lens for exposure without losing the focus.

Benefits for applications

The OptiFly Advantage: Unmatched Precision and Reliability in Laser Lithography

Achieving optimum resolution over large areas

Consistent cut-off resolution of a tool can only be achieved if every single step of the process is flawless. This starts with precise alignment of the UV laser beam along the Z axis on the resist. However, this is not enough: the focus must be maintained at all times if we are to write the large area patterns required by modern applications.

Fine placement of the focal plane enables advanced processing

Precise placement of the UV -laser spot within the resist layer is critical for writing the best resolution features. Further, control of the placement of focal plane at the top of the resist surface, within the resist layer, and at the resist substrate interface is critical for controlling the resist side-wall profile for various applications.

Adapting to the substrate type and topography

Our LBL tools address a wide range of applications, from advanced semiconductor processing and quantum computing chips to high-security holographic printing. Our OptiFly technology adapts to diverse substrates—including transparent, absorptive, reflective, or structured surfaces, even with significant height variations—by integrating optical and electronic control paradigms.

Structured wafers

OptiFly technology allows not only wafer-scale changes such as warpage and bow to be handled, but also higher-frequency topographies such as pre-existing structures, e.g., metal lines on a sapphire wafer.We can track ± 300 µm of height differences over a full wafer. By using various strategies to capture and utilize substrate height maps and optical autofocus signals together with the ability to control the red-laser power, the PICOMASTER can address the challenges posed by these complex substrates.

How it works

Inside OptiFly: The Hybrid Autofocus Revolution in Laser Lithography

Astigmatic Autofocus Strategy

The first part of our OptiFly technology depends on an astigmatic autofocus (AF) strategy. Our Laser Beam Lithography (LBL) systems use a collinear red laser that is co-focused at the same plane as the writing laser through the objective lens.

The autofocus beam is designed to be astigmatic, so that the focused spot is circular only at the point of focus. When it is defocused, it becomes elliptical and rotates. The reflected red laser is collected through the objective lens and projected onto a segmented quadrant photodiode (QPD).

By using the voltages generated across the photodiode quadrants when the beam is defocused, the system can precisely determine the location of the focus and align the laser. With an optical detection limit of 10 nm, the system takes 30 thousand measurements of the focus position every second during the exposure—that is, one measurement for every 15 microns of substrate length at the highest scan speed, roughly 1/6^th the width of an average human hair.

graphic showing the astimatic autofocus of OptiFly

Figure 1 – Astigmatic AF principle. A red laser spot is focused onto the same plane as the writing UV laser. The reflected image of the spot is projected onto the QPD. If the laser is in focus, the projection appears circular and all the quadrants generate the same voltage. If the laser is defocused, the image becomes elliptical and creates voltage differences across the opposing diagonal quadrants. This difference can be detected and used for capturing and maintaining the focus.

The Hybrid Autofocus Technology

The improvement of OptiFly technology over existing AF systems, whether optical or air-pressure-gauge based, is based on our hybrid approach to the AF challenge, which creates a more robust system than its counterparts.

The strength of this hybrid AF technology stems from a sensor fusion approach that combines the signals from precise lens position measurement by an optical encoder with the optical AF signal measured by the QPD. When combined with a closed-loop controlled lens actuator that can track and control the lens position, this approach yields a highly robust dynamic AF system architecture that can handle a broad variety of substrates and edge cases. The starting point involves capturing a height map of the exposure area at the beginning of each job in the job list queue. If the optical signal is lost due to a discontinuity (e.g., a particle, coating defects, trenches, vias, substrate edges, etc.) during exposure, the OptiFly system then takes over and adopts the estimated lens location based on the initial height map until the optical signal is recovered.

This technology allows us to overwrite native discontinuities such as existing structures on the substrate and over the edges, as well as overwriting undesired features such as particles and defects, without complete loss of focus.

Use case

OptiFly technology supports precise and stable lithography on large substrates such as complex wafers with structured surfaces or discontinuities, and substrates that present challenges such as bowing, warpage, or domed surfaces. Offering advanced autofocus and distortion compensation, this system ensures consistent focus across varying topographies. In addition, PICOMASTER systems featuring OptiFly technology excel in exposing small chiplets as small as 5 mm wide or potentially even smaller, thanks to their porous chuck option that maintain high accuracy without any risk of surface contact or loss of focus. This robust performance makes the technology ideal for handling intricate non-planar substrates; it supports precision lithography across challenging surfaces while maintaining the speed and reliability required for industrial-scale applications.

Application use cases