Process Engineering and Analysis

Free-standing thin films are used in wide range applications, including sensors, ultrathin electron and x-ray transparent windows and MEMS. When designing a thin film device, it is often important to know fracture properties of the thin films in order to ensure that the device will function without mechanical failures. However, measurement of fracture properties of thin films is challenging due to the need for specimen handling and alignment mechanical loads with nanoscale accuracy. To address these challenges we developed a simple technique in which thin film test samples are fabricated and tested on-chip. In this presentation, we discuss the development aspects encompassing the fabrication of test structures and the methodology to initiate controlled crack propagation. Using the developed technique, we achieved successful measurement of fracture energy in ZrSi_x and SiN free-standing thin films, showing good agreement with existing literature.

The SPTS Synapse has a unique high-density plasma source with a plasma density 10¹²-10¹³ (ten times higher than a conventional ICP source) designed for highly ion-assisted chemical reactions. The Synapse is therefore the ideal tool for high speed etching of optical/photonics devices, high-performance waveguide processing with extremely low sidewall roughness, and for high-precision pattern transfer into SiO₂ and Si_xN_y layers, and fused silica substrates. To ensure uniform pattern transfer into dielectric materials with a high CD control, the sidewall of the mask material profile should have a profile angle of 88° to 90° with a low sidewall roughness. Wafer-to-wafer reproducibility can be guaranteed by optical emission spectrometry and laser interference endpoint detection.

Status: 

• Etching mask layouts into Si_xN_y and SiO₂ (e.g., for DRIE and KOH processing) using Olin 907-17 as mask material
• Etch rate of SiRN: 250 nm min^-1
• Etch rate of SiO2: 350 nm min^-1
• Etch profiles are close to 88°

Current projects:

• Transfer of existing oxide/nitride etching recipes to Synapse
• OS – Deep (18 µm) SiO₂ stack etch
• LioniX – SiN/SiO₂ waveguide stack etch
• AQO – SiRN waveguides on sapphire
• Bronkhorst High-Tech – SiRN slit etch for channel fabrication
• MCS – Microfluidic channels in fused silica

Photonic integrated circuits (PICs) are a rapidly growing technology with applications in a variety of fields such as telecommunications, computing, healthcare, and sensing. To increase the functionalities of PICs and meet the demands of these diverse applications, the integration of active-passive material platforms is imperative. Rare earth ions doped into various host materials are a promising optical gain media due to the available wavelengths, flexibility processing techniques and host insensitive properties. Al₂O₃ is an excellent candidate as host material due to its broadband transparency, very low propagation losses, possibility of wafer-level deposition, and high rare-earth ion solubility which enables optical gain at different spectral ranges. In this presentation, we show the fabrication rare-earth ion doped Al₂O₃ waveguide amplifiers using reactive co-sputtering, electron beam lithography and reactive ion-etching. Additionally, we demonstrate the multi-layer integration with Si₃N₄ photonic circuits.

Pursuing three-dimensional (3D) structuring has empowered the development of techniques permitting the shaping of matter across length scales. Among the additive manufacturing approaches, two-photon lithography (TPL) emerged as an exclusive method facilitating the production of freestanding features with (sub-)micrometer fidelity, ideal for the fabrication of optical elements and systems (hereafter micro-optics). A key component in TPL that can pave the path for printing 3D micro-optical elements is a photoresin. However, organic-based photoresin restricts chemical stability and lacks a high refractive index (n), typically <2. Using metal/metalloid-rich photoresists can potentiate the production of (sub-)micrometer geometrically shaped glass and ceramics of high chemical stability and n ≥2, which are desired properties for light propagation control along the engineered medium. This session discusses the formulation of metal/metalloid photoresins, followed by a few examples of TPL-printed ceramic architectures.