The current demands from optical interconnect, LIDAR technology or face recognition is driving the VCSEL industry to grow faster. VCSEL manufacturing is rapidly scaling up across the world and the VCSEL fabrication process has to achieve ever higher yield and quality. Applications, such as 3D sensing, focus on maximum power conversion with arrays of VCSELs for higher combined output power. Within an array, the threshold current and differential quantum efficiency have to be uniform from laser to laser. This requires very good control of epitaxy but also very good control of the shape of the mesa. As the need for denser array increases, challenges on uniformity, line width and aspect ratio emerge.
With a strong process expertise and extensive device understanding, Oxford Instruments Plasma Technology has developed advanced plasma processing solutions to deliver the device performance and yield demanded by the VCSEL market. In this white paper, we focus on how to best control the geometry of the mesa for wafer size up to 150mm. We review the key requirements for achieving either a tapered or vertical profile with precise control of the depth of the mesa.
Main Fabrication Steps of VCSEL Structures
The simplicity of the VCSEL structure allows for high volume manufacturing at very efficient cost. Compared to edge emitting lasers, more VCSELs can be manufactured per wafer and on larger wafer sizes. The vertical fabrication of VCSELs also allows for a high level of integration of additional components. Photo detectors, mirrors, circuitry and other components can easily be integrated onto the structure to achieve chip on board (COB) technology. As the technology evolves, multiple designs have been developed for specific applications. Here we take a look at a simplified process flow to design the laser cavity.
Multiple processing steps are required to fabricate VCSELs. The table in Figure 1 below gives a simplified breakdown of each step of fabrication of GaAs based VCSEL, highlighting the Oxford Instrument solution for relevant steps. The PlasmaPro 100 delivers uniform process on wafers up to 200mm. The VCSEL market is currently moving towards 150mm so most of the work demonstrated here is focused on 100mm to 150mm wafer size.
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This information has been sourced, reviewed and adapted from materials provided by Oxford Instruments Plasma Technology.
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