In semiconductor processing, packaging is a critical step in finishing a final product. After completing the dicing process to singulate dies from a larger substrate, the cut dies generally remain affixed to dicing tape. It can be difficult to manually remove the dies without scratching or rubbing against one another, causing chipping or other damage. A die expander allows for the tape to be stretched on expander rings, separating the dies for easier removal or shipping.
We are happy to announce the addition of a Hugle Model-1810 Die Matrix Expander to the nanoFAB's tool lineup. This expander is capable of accommodating diced specimens up to 150 mm in diameter. It is equipped with a heated chuck, allowing for easier separation of the dies without delamination from the tape, as well as a preheat timer, which helps with process repeatability. The stage expansion distance is adjustable, allowing for customized spacing between the dies. The system also includes an automated cutter tape separation system for ease of use. Previously, without the use of this tool, users in our facility needed to mount diced 150 mm wafers onto the expander ring by hand, a task that often required two people to do!
We hope that the addition of this new system in our toolset will facilitate the final processing and packaging of the many devices fabricated in our open-access facility. Please submit an equipment training request via LMACS if you wish to get trained on the die expander. For more information, please contact Breanna Cherkawski.
Please see below for some videos of the tool in action:
Optical Emission Interferometry (OEI) in the Plasma-Therm Versaline PECVD
Overview
In plasma-enhanced chemical vapour deposition (PECVD) tools, the deposition rate of deposited films can often fluctuate with relative gas concentrations, material build-up on the chamber walls, and other mechanisms that make timed depositions inconsistent. To combat this problem, a simple technique called Optical Emission Interferometry (OEI) can be used. OEI provides a more robust form of deposition control based on the interference of light reflected off of the growing film to precisely hit target film thicknesses.
OEI uses similar principles to other interferometric tools like the Filmetrics F50-UV; the intensity of light at a single wavelength reflected off of a thin film will vary depending on the wavelength of light and the optical thickness of the film. This is due to the relative phase difference between light reflected off the top surface of the film and at the film-substrate interface, i.e., conditions of constructive and destructive interference (shown in Fig. 1). Across a broad spectrum of wavelengths, this can be used to fit to both refractive index and film thickness robustly (as Filmetrics does). However, if the intensity of light reflected off of a growing film is recorded continuously, the intensity at a "single" wavelength will oscillate approximately sinusoidally as the thickness increases (satisfying constructive and destructive interference conditions at specific thicknesses)—this is the fundamental premise of OEI. By noting when the extrema occur during film growth, the period of this oscillation (T) can be used to measure the deposition rate of the film, since T is set by the phase conditions for constructive/destructive interference. T = λ/(2n); where λ is the wavelength of interest and n is the refractive index of the material at this wavelength.
Figure 1. Phase conditions for destructive and constructive interference of light reflected off of a thin film, from H. G. Tompkins, and J. N. Hilfiker, Spectroscopic Ellipsometry: Practical Application to Thin Film Characterization (Momentum Press, 2016).
To use OEI in the Plasma-Therm Versaline PECVD, light produced by the plasma is reflected off of the growing film and collected by a spectrometer centred above the wafer for plasma monitoring. The Plasma-Therm EndpointWorks software package is then used to monitor the evolution in time of the spectral intensity emitted from the plasma within a narrow range of wavelengths. Choosing a range that encompasses an emission line of a typical gas/radical species within the plasma produces the oscillatory data shown in Fig. 2. Values of T are calculated based on known values of n and λ to give an estimate of the deposition rate based on the spacing of the extrema. Thus, in order to function correctly, each OEI recipe requires the user to have knowledge of both the growing film (single wavelength refractive index) and of typical optical emission lines (usable wavelengths) within the plasma.
Figure 2. EndpointWorks Thickness Detector data for a growing SiO2 film.
Wavelength choice
The choice of what wavelength to use for OEI depends on the chemistry of the plasma in question, since each gas/radical species emits light at different wavelengths (depending on its electronic transitions), and thus the available wavelengths will differ for each recipe. Potential emission lines are further limited if the gas species characteristic of an emission line is consumed during the reaction. The intensity of these reactant emission lines will fluctuate as the film grows and as the local gas concentration changes. In contrast, the intensity of an emission line of an inert gas (He, Ar, or N2 are often used to dilute the reactants) will be much more stable, and will provide a reduction in noise in the reflected light. This leads to a more clearly defined periodic signal, where the extrema can be easily identified in software. Additionally, since variation in T is linear with the wavelength of light used, the choice of shorter wavelengths will reduce the period of oscillation, lending the OEI method more sensitivity and flexibility to accurately measure thinner films. Note, for films that are optically absorbing (e.g. a-Si and Si-rich nitrides), the film will absorb more strongly at shorter wavelengths, decreasing the amplitude of the oscillation as the film grows. Ultimately, this decay reaches a point where extrema cannot be identified past a certain thickness. A general rule of thumb is to choose the shortest wavelength inert gas emission line that is not strongly absorbed by the depositing film. A typical spectrum collected during deposition is shown in Fig. 3, where a N2 emission line at ~333 nm is highlighted, being suitable for the gas chemistry involved. For more details on choosing an emission line appropriate for your deposition, please see the Plasma-Therm Versaline PECVD OEI recipe development How-To on the nanoFAB's Confluence Knowledge Base.
Figure 3. Typical plasma emission spectrum (as measured on the Versaline's integrated Ocean Optics spectrometer) for the deposition of Si-rich nitride. Inset: full-width at half-max (dashed lines) of the N2 emission line centred at ~333 nm.
OEI controlled deposition recipes are currently qualified for SiO2 Dep ("OEI SiO2 Dep") and Stoichiometric Nitride ("OEI Stoichiometric Nitride") recipes, with an OEI recipe in progress for the Si-Rich Nitride. For user-developed films that differ from these established recipes, users are welcome to qualify their own OEI recipes following the Step-by-step instructions in the linked OEI recipe development How-To. If you encounter problems setting up your OEI recipe on EndpointWorks, please contact Tim Harrison (tr1@ualberta.ca).
AML Wafer Bonder now available for training
The nanoFAB is pleased to announce an upgrade to our wafer bonding and packaging area, with the recent installation of a wafer bonder from Applied Microengineering Ltd (AML). The AWB-04 wafer aligner-bonder from AML offers a wide range of bonding techniques and process flexibility. Of particular note is its in situ alignment capability, allowing users to verify correct alignment as the wafers are being brought into contact.
Bonding techniques include:
Anodic (borosilicate glass to Si)
Direct (Si to Si)
Eutectic (Si to Si or Si to glass with intermediate metal layer)
Thermocompression (bonding between metal films deposited on both substrates)
Other custom bonding techniques
Technical features:
Up to 150 mm wafer sizes (100 mm and 150 mm hardware available)
In situ alignment (visible and IR) with 1 µm accuracy; manual and automatic (image recognition) alignment procedures available
High vacuum (10-6 Torr)
Wafer separation of 30 mm
Independent platen temperature control, up to 560 °C
Radical activation (RAD) for in situ surface cleaning and activation
Bonding forces up to 40 kN
Anodic bonding voltages up to 2.5 kV, current limits up to 8 mA
Triple-stack anodic bonding
Wafer edge clamping (no contact on bonding surfaces)
Application Examples
Anodic Bond: borosilicate glass to Si
Cross-sectional SEM (left) and TEM (right) images of bonding interface.
Si–Si Direct Bond: in situ RAD + low-temperature anneal
TEM images of the bonding interfaces of silicon wafers after a low-temperature (250 °C) anneal performed in the AWB-04 chamber without breaking vacuum. The thin amorphous native SiO2 layer can be seen along the interface.
Si–Si Direct Bond: in situ RAD + external high-temperature anneal
TEM images of the bonding interfaces of silicon wafers after a high-temperature (1100 °C) anneal performed in Tystar General Anneal (Tube 6). The thin amorphous native SiO2 layer can be seen along the interface, but has diffused into the bulk Si layer.
Au–Au Thermocompression Bond: Si to Si with Au interlayers
SEM images of silicon wafers bonded via Au–Au thermocompression bonding: full wafer cross-section (left) and close-up of bond interface (right). Patterned Au films are deposited on Si wafers and bonded using moderate temperatures (~300 °C) and high pressures (~7.5 MPa). Images courtesy of Jones Microwave Inc. and RM3.
If you are interested in using the AML wafer bonder in your work, please submit a request through LMACS to receive training. If you have any questions, please feel free to contact Scott Munro or Aaron Hryciw.
New Spray Coating Tool Available
We are happy to announce a new addition to our fabrication tool lineup: a Sono-Tek ExactaCoat Spray Coater. This tool is located in our recently renovated 10k Lithography area (ECERF W1-031); please stay tuned over the coming months as we add more photolithography capabilities to this labspace.
The ExactaCoat, an ultrasonic spray coating system, can accommodate specimens up to 300 mm in diameter. This tool is primarily used for photoresist coating in situations where conventional spin coating is impractical or yields poor results: specimens that are too fragile, exhibit large topographical variations, or possess irregular shapes.
The spray coater offers a particular advantage for specimens where topography presents a challenge to achieving good film uniformity during spin coating: examples include MEMS or microfluidic devices with deep (tens to hundreds of µm) features etched via DRIE or KOH/TMAH. Process development is currently underway to formulate recipes suitable for coating deep and/or high aspect ratio topography wafers. Additionally, spray coating is a valuable technique for those looking to apply photoresist as a dicing protect layer on extremely fragile or through-etched substrates that are not compatible with spin coating.
Sono-Tek ExactaCoat Spray Coater
Schematics of the spray coating process (MicroChemicals)
The spray coating process uses high-frequency (ultrasonic) mechanical vibration that is transferred to the liquid in the nozzle. The standing waves created in the liquid are broken up as the liquid exits the nozzle—this aerosolised liquid is then dispensed onto the surface of the specimen as a fine mist.
To coat an extended specimen such as a wafer, the spray of atomised resist is rastered across the work area in overlapping stripes. This is illustrated in the following videos, where a cleanroom wipe is used to show the sprayed resist more clearly.
After spray coating a wafer with resist and softbaking, it may be exposed and developed to complete a photolithography process. The following optical microscope images illustrate some preliminary results of photolithography on Si wafers, showcasing excellent film uniformity and achieving lateral feature sizes as small as 5 µm.
Photolithography using spray coating: Si wafers spray coated with a ~4.5 µm thick film of AZ 1505, exposed in a contact mask aligner, and developed. The smallest feature size pictured in each image is 5 µm.
We are thrilled to introduce this new capability, along with the array of associated applications it makes possible. If spray coating is a technique you feel would be beneficial to your work, please submit a request through LMACS to receive training. If you have any questions, please do not hesitate to contact Breanna Cherkawski or Aaron Hryciw.
Raith_GDSII toolbox documentation now on Read The Docs
Now in its tenth year of existence, the Raith_GDSII MATLAB toolbox makes it easy to generate patterns for Raith electron-beam lithography (EBL) and focused ion beam (FIB) applications using MATLAB. It can also be used to generate “plain” (non-Raith-dialect) GDSII files for non-EBL applications such as printing photomasks or direct-write laser lithography exposures. This open-source project is maintained by the nanoFAB, may be downloaded from GitHub.
As of the most recent update, the technical documentation for the toolbox is now hosted online on Read the Docs, as opposed to the PDF user manual which served as documentation for previous versions.
This switch to online documentation ensures the documentation is always up to date (rebuilt with each GitHub commit), and includes quality of life improvements such as copy-to-clipboard buttons on all code block examples and a “search as you type” feature. This update also includes a small bugfix relating to outputting FBMS path elements with curvature in “plain” GDSII dialect, as well as several typographical edits to the documentation content.
We are excited about the potential of this updated documentation format to simplify and enhance both the initial learning and ongoing utilisation of the Raith_GDSII toolbox, for anyone interested in EBL, FIB, or other lithographic techniques. For more information, please contact Aaron Hryciw.
Kurt J. Lesker 150LX ALD system now open for training
The nanoFAB is pleased to announce that our newly installed and commissioned KJLC 150LX Atomic Layer Deposition system is now fully operational and available for training to all nanoFAB users. The ALD offers excellent uniformity and controlled growth of a variety of films on an atomic scale. Its high-vacuum load-lock and UHV-type sealing, combined with near-constant high-purity Ar flow, enable high-purity process conditions and excellent quality films.
Main system features include:
Single wafer transfer load-lock
Substrate heating up to 500 °C
150 mm platen, with an available carrier for samples <150 mm
Thermal and plasma-enhanced (PE-ALD) processes available
In situ film growth monitoring using Film Sense FS-1EX multiwavelength ellipsometer
The KJLC 150LX ALD is available to users for self-use (after training) and fee-for-service work. Any users interested in getting trained on this tool should submit a training request via LMACS. If you have any questions, please contact Aaron Hryciw (ahryciw@ualberta.ca) or Scott Munro (smunro@ualberta.ca).
