Discover Vertical Cavity Surface Emitting Lasers

Infrared lighting, proximity sensors, high-resolution video displays, atomic clocks, and facial recognition technologies are just some of the innovative uses for vertical cavity surface emitting lasers, or VCSELs.

Discover Vertical Cavity Surface Emitting Lasers

Image Credit: FormFactor Inc.

High-Volume Manufacturing of Laser Products Possible

VCSELs are typically advantageous due to their low cost, small footprint, and optical efficiency. They also have the benefit of wavelength stability over temperature. Additionally, rather than installing the optical elements separately for each VCSEL, it is possible to bond a VCSEL wafer with various optical components before separating the bonded wafer.

There is, therefore, a potential for the low-cost mass production of laser products. VCSELs have the added capacity to be tested and characterized before the wafer's separation, which is a significant advantage over edge-emitting semiconductor lasers. As a result, quality issues can be identified early on.

VCSEL—What Is It Actually?

VCSELs are semiconductor lasers wherein the emitted light emerges perpendicular to the chip surface. Utilizing either molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD), a complicated multilayer structure is applied to the substrate to create a VCSEL.

The photons produced by the active layer in the epitaxial layers are caught between two Bragg reflectors (DBRs). To increase amplification, the light is reflected back and forth numerous times through the active surface using the Bragg reflectors as mirrors.

With a GaAs/AlGaAs material combination, VCSELs typically provide output powers between 0.5 and 5 mW, with the most frequent emission wavelengths falling between 750 and 980 nm.

Considerably higher powers can be produced with VCSEL arrays. A 2D VCSEL array with thousands of emitters spaced a few tens of micrometers apart can compete with diode bars and even diode stacks based on edge-emitting semiconductor lasers by generating several tens of watts of continuous radiation. Adding more emitters makes it simple to increase the output power.

Modern Surface Measurement Technology

The best options for these various, complex applications are all-in-one solutions. They must be able to handle conventional, thinned, and bonded wafers as well as film frames and be capable of meeting measurement criteria for a wide range of processes.

Furthermore, MicroProf® FS provides extensive measurement solutions for tracking a variety of compound semiconductor substrates, including GaAs, InP, SiC, GaN, ZnO, and transparent materials.

The Technical Solution

The MicroProf® FS is a fully automatic wafer metrology instrument with a variety of uses in different stages of the manufacturing process, which include:

  • Defect and haze mapping after epitaxy with great sensitivity to significant sub-micrometer faults
  • Thickness of dielectric layers, step height and width of metallization,
  • TTV, thickness, roughness, and roll-of-amount (RoA) measurements following wafer grinding
  • Measurement of wafer thickness
  • Determination of critical dimensions (CD) and etching depth
  • Bow and stress in epi process control
  • Bond wafer taper and the examination of adhesive layer flaws
  • The acquisition of reflection spectra of Bragg reflectors (DBRs)

The MicroProf® FS provides exceptional flexibility and universality, thanks to its modular multi-sensor concept. This makes it ideal for several measurement tasks in the production of VCSELs. This is the critical point for VCSEL producers that continually modify their research programs to take advantage of new materials and cutting-edge nano-scientific theories.

Conversely, the FormFactor FRT MicroProf® DI optical inspection tool enables wafers that are structured and unstructured to be inspected during the production process.

The MicroProf® DI offers measurement solutions for various applications by integrating 2D inspection and metrology, including defect inspection and wafer-level metrology for micro-bumps, RDL, overlay, and through silicon via (TSV) in a single measuring tool.

The Base Component

The well-known MicroProf® 300 is the essential component. Through a hybrid measuring concept, this multi-sensor measuring tool increases the precision of measurements on samples for which a single sensor or a single measuring principle is insufficient. It also allows for the measurement of wafers in various process phases.

Discover Vertical Cavity Surface Emitting Lasers

Image Credit: FormFactor Inc.

These measurements could be made using various topographical and (layer) thickness sensors, all entirely automated by a single recipe, depending on the task. These sensors automatically combine multiple pieces of information under the control of internal software created by FormFactor FRT, creating new information that is not immediately available.

The Software

The FormFactor FRT Acquire Automation XT software controls the tool, which complies with SEMI standards. Using this software, measurements can be made according to a recipe, and comprehensive data analysis is possible, including the automatic determination of VCSEL parameters.

From a selection of packages, users may choose the measurement and assessment procedure that is most appropriate for a specific measurement task. A layout wizard with a graphical user interface (GUI) can assist them in filling in the measurement positions for recurring structures. Additionally, it is optional to use pattern recognition to precisely align the samples.

This software provides a wide range of features, including fully automatic measurement with a single button operation and integration into production control systems, such as via a SECS/GEM interface, in addition to manual measurement on the tool.

It is simple to program numerous measurement tasks with various sensors to be performed sequentially as a measurement sequence. This also includes intelligent algorithms to execute processing, measurement, and analysis.

The output and display of the results in the form of reports and their exportation in various data formats are also included. Customers also gain from pass/fail level classification and sample statistics at the wafer and die level.

The Perfect Workhorse

With almost maintenance-free hardware components and a wafer handling system within an Equipment Front End Module (EFEM), the MicroProf® FS offers a high throughput and is the perfect workhorse. Users can quickly recoup their investment expenditures with the MicroProf® FS and keep up with the VCSEL industry’s rapid development.

This information has been sourced, reviewed and adapted from materials provided by FormFactor Inc.

For more information on this source, please visit FormFactor Inc.

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