How to Make Better Photonic Measurements

FormFactor recognizes that a test engineer’s main objective is to make measurements. An integrated, verified solution will mean that engineers no longer waste valuable time on prolonged development projects.

FormFactor’s SiPh Measurement Assistant enables faster time to more accurate measurements and reduced cost of test.

FormFactor has developed all of the tools, fixtures and calibration techniques that allow engineers to measure photonic devices in just days rather than months or years.

FormFactor’s Autonomous Silicon Photonics Measurement Assistant is a dynamic solution that facilitates rapid changeover for a range of testing needs from single fibers to arrays and from vertical coupling to edge coupling.

FormFactor’s Photonics Integration Kit and the innovative  OptoVue Calibration Kit will offer users production-proven, optimized optical measurements immediately after installation.

FormFactor’s CM300xi Probe Station: Highly-stable and robust 300 mm platform for optical probing

FormFactor’s CM300xi Probe Station: Highly-stable and robust 300 mm platform for optical probing. Image Credit: FRT Metrology

Industry-First Features

  • Automated Optical Positioning Alignments and Calibrations
  • Highly Flexible Solution For Single Fibers/Arrays and Edge/Vertical Coupling
  • Integrated Z-Displacement
  • In-Situ Calibrations and Singular Die Testing with Optovue Pro
  • Validated Integration, Verified Performance
  • Wafer and Die-Level Edge Coupling 

Silicon Photonics Measurement Assistant on FormFactor

Silicon Photonics Measurement Assistant on FormFactor's 200 mm probe station SUMMIT200.  Image Credit: FRT Metrology

OptoVue / OptoVue Pro - Faster Time to Data with Real-Time In-Situ Calibration

 Features 

  • Advanced Calibration Technologies
  • Enables Autonomous Measurements
  • In-Situ Power Measurements
  • Real-Time In-Situ Calibrations
  • Singulated Die Testing
  • True Die-Level Edge Coupling 

With its OptoVue and OptoVue Pro, FormFactor can offer innovative technology advancements for wafer and die-level photonics probing. This feature incorporates state-of-the-art calibration technologies with enhanced viewing directions and a considerable number of additional features that facilitate faster run times to more accurate measurement results. 

Positioned in auxiliary chuck locations on the CM300xi and SUMMIT200, OptoVue and OptoVue Pro allow calibrations to be conducted in-situ without the need to remove the test wafer to place a calibration wafer on the chuck.

This CalVue feature facilitates straightforward calibrations without operator intervention, leading to faster measurement times and generating reduced costs of tests. 

OptoVue Pro is comprised of a feature-rich set of tools for optical probing such as DieVue for die-level probing of singular photonic devices, ProbeVue for measuring and inspecting fibers and fiber arrays, and PowerVue for measuring the probe tip’s laser power. 

Image shows OptoVue Pro on a CM300xi.

Image shows OptoVue Pro on a CM300xi. Image Credit: FRT Metrology

CalVue

  • In-situ calibration for Z-Displacement and optical positioning 

PowerVue

  • Enables in-situ power measurements at the measurement plane of single fiber and fiber array High sensitivity photodiode
  • Measure and remove laser to fiber tip path loss Power Measurements up to 40 mW  

ProbeVue

  • Find initial array coupling offset position from corner
  • Upward looking probe inspection function for single fibers, fiber arrays, DC and RF probes 

DieVue

  • Customizable die holder
  • Singular die test
  • Up to 25 x 25 mm die
  • Vacuum secured
  • Vertical and edge coupling 

 

Table 1. Source:  FRT Metrology

 
Feature OptoVue Pro OptoVue OptoVue200 Pro OptoVue200
CalVue (replaceable with DieVue)
PowerVue - (placed on front left, flexible
location in case of upward looking camera)
-
ProbeVue -   -
DieVue - (replaceable with CalVue) -

 

Probe inspection with ProbeVue

Probe inspection with ProbeVue. Image Credit: FRT Metrology

In-situ power measurements with PowerVue

In-situ power measurements with PowerVue. Image Credit: FRT Metrology

Pull-out chuck with OptoVue Pro in the auxiliary chuck position - CM300xi

Pull-out chuck with OptoVue Pro in the auxiliary chuck position - CM300xi. Image Credit: FRT Metrology

Pull-out chuck with OptoVue Pro 200 in the auxiliary chuck positions - SUMMIT200

Pull-out chuck with OptoVue Pro 200 in the auxiliary chuck positions - SUMMIT200. Image Credit: FRT Metrology

Edge Coupling - High Coupling Efficiency for High Bandwidth 

Features 

  • Automated Fiber-to-Facet Alignment
  • Ease of Use for Less Experienced Users
  • Fiber Collision Avoidance
  • Highest Accuracy in Test Results
  • Lowest Coupling Loss
  • Optimization of Gap Between Fiber Tip and Waveguide 

Horizontal Die-Level Edge Coupling 

The most effective coupling efficiency for high bandwidth applications can be accomplished by ensuring fibers/arrays are as close as possible to the exposed waveguide facet(s) via horizontal die level edge coupling. 

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

True edge coupling facilitates accurate simulation of real-world conditions with device performance closely resembling the final application. 

FormFactor offers the only solution on the market that facilitates sophisticated automated alignment for horizontal die-level edge coupling, employing exclusive automated fiber-to-facet alignment techniques and significantly limiting the risk of fiber damage with collision avoidance technology. 

Specialized software algorithms like AlignOpticalProbes3D facilitate the optimization of the fiber-to-facet gap versus simultaneous maximum coupled power at both the input and output. There is no possible alternative that enables users to fix the positioning hardware calibrated in the YZ plane and ready to conduct edge coupled optical optimizations. 

Wafer-Level Edge Coupling 

Wafer-level edge coupling can now be realized using a new groundbreaking combination of hardware and software features to coordinate and optimize fibers/arrays in a wafer-level trench. 

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

A complete suite of software alignment algorithms facilitates YZ optimization scans in a wafer trench while tapered lensed fiber holders supply a low approach angle in relation to the wafer surface. This allows accurate probe alignment in the trench as close as possible to the facets, reducing coupling losses with minimal trench dimensions. 

The solution streamlines setup even for less experienced users, repeatable measurement results as a result of novel fiber-to-facet gap alignment technology, and limited risk of damaging fibers with collision avoidance technology. 

Industry-Leading Edge Alignment Features 

Measure3DCoupling 

Measure3DCoupling can carry out successive area scans and stepping moves along the coupling axis, compiling a 3D image of power coupling. The technology is useful in a number of applications, such as detecting DUT contamination, detecting fiber damage, measuring the focal length of the lensed fiber, etc. It is also applicable to both edge and vertical coupling. 

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

AlignOpticalProbes3D 

AlignOpticalProbes3D attempts to determine the optimum gap for both input and output fibers that produces maximum coupled power. 

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

AlignOpticalProbesEdge 

AlignOpticalProbesEdge conducts vision-based gap alignment on numerous selected probes and then scans the YZ area while recentering as necessary. 

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

AlignOpticalProbeGap 

AlignOpticalProbeGap conducts a vision-based gap alignment on a single probe in XY, moves to probe height in Z and prepares for an area scan. 

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

Vertical Coupling - Wafer-Level Coupling to Surface Gratings 

Integrated Alignment Features 

  • Align Optical Probes
  • Optical Scan Data Analysis
  • Optical Rotation Scan
  • Optical Tracking
  • Search First Light 

Incident Angle Calibration  

Now established as the industry standard, FormFactor’s technology is used for vertical coupling to wafer-level grating couplers. No other solution on the market is able to achieve calibration of the positioning hardware aligned with the probe station and ready to conduct die-to-die optical optimizations in minutes. 

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

With unique calibrations like Pivot Point, the optimal point of minimal translation at the fiber/array tip is determined automatically. Utilizing this Pivot Point, FormFactor’s Incident Angle Optimization routine allows users to establish what position is best to optimize coupling efficiency. 

Understanding how the optimized incident angle compares to the designed incident angle can allow users to determine fab or other process defects. 

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

Incident Angle Optimization

Incident Angle Optimization. Image Credit: FRT Metrology

Thermal Capability - Enables Autonomous Calibrations at Multiple Temperatures

Features 

  • Autonomous Calibrations at Multiple Temperatures (-40 °C to +125 °C)
  • Dark, Shielded and Frost-Free
  • Minimized Air Flow Impact on Fibers/Arrays
  • Reliable and Accurate Measurements
  • Unique Window for Easy Setup

Conducting optical device measurements at various temperatures is crucial when it is necessary to comply with particular industry compliance standards, regardless of whether it is devices for data centers that must be tested in high-temperature environments or automotive devices that necessitate both hot and cold testing. 

The challenges associated with testing at numerous temperatures include system drift, air flow impact on the extremely sensitive fibers/fiber arrays and the necessity for re-calibration. FormFactor’s unique SiPh TopHat is the only solution that offers a completely sealed, dark, shielded and frost-free environment with complete thermal capacities from -40 °C to +125 °C. 

Only the SiPh TopHat facilitates the minimization of air flow impact at cold temperatures, thereby protecting the fibers/fiber arrays and allowing stable and repeatable measurement results. 

In combination with the innovative OptoVue/ OptoVue Pro and intelligent machine vision algorithms, the system allows truly hands-free, autonomous calibration and re-calibration at various temperatures. 

Thermal calibration intervals are configurable as the influence of thermal drift on fibers fluctuates over the desired temperature range. 

The SiPh TopHat was developed to prevent stiction which reduces motorized positioner accuracy. Cable management is integrated into the mounting plates for both fibers and positioner cables. A specialized ITO-coated TopHat window enables the simple assembly of probes without having to open the thermal chamber. 

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

CalVue - Exclusive Automated Calibrations

Calibration Functions

 Automatic Pivot Point Calibration

  • Motor Calibration
  • PZT Calibration
  • Planarity Calibrations
  • Theta Calibrations
  • Z-Displacement Calibration  

The system can be quickly set up to perform the ultimate goal of making precise and reliable measurements on devices.

 FormFactor has developed a pioneering set of automated functions that perform critical calibrations of the optical positioning system to the probe station and step-by-step wafer to probe height training - even for combined optical and electrical probing.

 With CalVue, part of OptoVue and OptoVue Pro, FormFactor moves these industry-exclusive automated calibration functions into the probe station.

 Utilizing uniquely designed retro-mirror technology, the objective lighting of eVue can be used to view all aspects of the fiber/array without external light. This eliminates the need for oblique lighting and enables real-time in-situ automated machine vision calibrations.

Horizontal view of single fiber with CalVue

Horizontal view of single fiber with CalVue. Image Credit: FRT Metrology

Horizontal view of fiber array with CalVue

Horizontal view of fiber array with CalVue. Image Credit: FRT Metrology

Proven Performance - Automated Performance Verification

 Verified Parameters  

  • Coupled Power Repeatability
  • Chuck Calibration to Optical Positioning
  • Hexapod Motion Calibrations
  • PZT Motion Calibrations 

FormFactor’s development of an automated test methodology exhibits the full performance of the positioning solution calibrated to the probe station with just one click of a button. 

The performance verification script guarantees that all 9 or 18 Axis’ of the positioning solution are calibrated accurately to the 4 Axis’ of the probe station by measuring the coupled power repeatability of the entire system. 

A total of 900 measurements are conducted at nine varying waveguides in three reticles of FormFactor’s Silicon Photonics Test Coupon wafer. Between each of the 100 measurements conducted at each waveguide, all solution elements are relocated, including the wafer chuck, hexapod stages and piezo stages. 

After each step has been carried out, the system is verified to measure the coupled power results at each waveguide to within less than 0.3 dB across these 100 measurements. This kind of measurement performance clearly demonstrates the integrated performance and ruggedness of FormFactor’s Autonomous Silicon Photonics Measurement Assistant. 

<0.3dB coupled power repeatability results

<0.3dB coupled power repeatability results. Image Credit: FRT Metrology

FormFactor Silicon Photonics test coupon wafer

FormFactor Silicon Photonics test coupon wafer. Image Credit: FRT Metrology

SiPh-Tools and Photonics Controller Interface - Powerful Software Interfaces 

Uniquely Developed Features  

  • Automated Alignment Functions
  • Calibration Wafer Verifications
  • Measurement Position Training
  • Optical Alignment Verifications
  • Wafer Training Sub-Die Management 

FormFactor’s SiPh-Tools is a unique software package that includes an expansive toolset for facilitating optical probing. By incorporating probe station machine vision capabilities with optical positioning and test equipment, SiPh-Tools is able to automate manual tasks. 

From performing optical scans during die-to-die stepping to training measurement positions, SiPh-Tools offers the performance needed to quickly gather data from devices. 

One example is the new Search First Light feature that utilizes outward moves of the hexapod while the nanocube continuously stirs in a circular path looking for a measured power signal above a set threshold. SiPh-Tools also has an extensive range of tools for capturing, logging, and interpreting the data that users collect. 

SiPh-Tools provides the communication link between multiple applications, including Velox and PCI.

SiPh-Tools provides the communication link between multiple applications, including Velox and PCI. Image Credit: FRT Metrology

Photonics Controller Interface (PCI)

 FormFactor has developed the Photonics Controller Interface (PCI) application which supplies a graphical user interface that facilitates user flexibility for manual control of the optical positioning system. 

This interface is feature-rich and can also be used to configure scan parameter arrangements and conduct initial optical alignment functions, among several other functions. Once aligned, all calibration functions are automated and carried out using SiPh-Tools.

SubDie Mapping

SubDie Mapping of sub-die optical and electrical measurement locations for automated stepping to several substructures within a die can be challenging.

However, FormFactor has designed a function in SiPh-Tools that streamlines this task by allowing the user to map between wafer, positioner and microscope coordinate systems so that sub-die probing locations can be accurately determined in wafer (e.g., CAD) coordinates.

The positioner and scope positions required to probe these locations can be mapped using a set of coordinate references. Once training of references is complete, all optical and electrical positioners in the system and the scope can be moved automatically to arbitrary probing locations that have been pre-determined in wafer coordinates.

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

Photonics Controller Interface - controls manual positioning, scan parameter configuration, and initial optical alignment functions.

Photonics Controller Interface - controls manual positioning, scan parameter configuration, and initial optical alignment functions. Image Credit: FRT Metrology

Reconfigurable Fiber Arm - Perfected Alignment with Precision Z-Displacement

Reconfigurable Fiber Arm 

  • Configurable Between Single Fibers and Fiber Arrays
  • Flexibility for Engineering and Volume Environments
  • Supports a Wide Range of Incident Angles
  • Z-Displacement Kit Includes Custom Light Weight Close Proximity Integrated Sensors

 The fiber arms’ rigid design minimizes resonance, enhances scan rates and improves stability. A replaceable fiber holder enables users to switch between different incident angles as well as between single fibers, fiber arrays and edge coupling holders.

 After fiber holders have been changed, FormFactor’s automated calibration routines have the capacity to get users up and running in a matter of minutes. The built-in, customized nanometer-accuracy Z-Displacement sensor increases the testable area of the wafer with its minimal footprint. 

Its close proximity and lightweight design relative to the fiber/arrays ensure accurate and repeatable data collection. FormFactor‘s custom setup fixture facilitates rapid changeover between the different fiber holders and includes the initial setting of the Z-Displacement sensor. 

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

Fiber/Array Holders - Comprehensive Selection for Specific Test Requirements 

Features  

  • Compatibility
  • Coupling Holders
  • Horizontal Edge Coupling Holders
  • Offset Angles
  • Single Fibers Fiber Arrays
  • Vertical Coupling Holders
  • Wafer-level Edge  

How to Make Better Photonic Measurements

Image Credit: FRT Metrology

Table 2. Source:  FRT Metrology

  CM300xi SUMMIT200
Autonomous Calibration at Multiple Temperatures
Die-Level Edge Coupling
Wafer-Level Edge Coupling
Grating Coupling
OptoVue / OptoVue Pro
Thermal Capability
Semi-auto
Fully-auto

 

“GF’s silicon photonics leverages standard silicon manufacturing techniques to improve production efficiency and reduce cost for customers deploying optical interconnect systems. We’re excited to be at the forefront in deploying new test capabilities, including wafer level solutions to ramp this important technology.”

This information has been sourced, reviewed and adapted from materials provided by FRT Metrology.

For more information on this source, please visit FRT Metrology.

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