Key VCSEL Application Challenges

Temperature and Reactivity

Current technologies operate at higher temperatures or use highly reactive non-compatible oxidants that do not adequately form to the surface. New oxidants are required to deposit high quality oxide films at low temperature and not cause sub-surface oxidation. Thermal ALD is preferred because it leads to conformal deposition on 3D surfaces.

Interfacial Defects Caused by Island Growth

ASD requires fast nucleation and initiation of film growth with minimal cycle delay. Water can require up to 7 cycles to deposit the equivalent of one monolayer. This leads to non-uniform growth and interfacial defects. Microdroplets are common, staining the wafer surface and increasing island growth.

Solving Key VCSEL Manufacturing Challenges

Damage-Free Oxidation

Protect VCSEL structure from defects by using water vapor that is free of microdroplets and particles. Control key process parameters including water vapor temperature and flow rate so that structures such as sidewalls are not compromised.

Controlled Oxidation Rate

Oxidation rate is typically dictated by material composition, process temperature, and oxide source attributes. Design in a water vapor delivery system with precision control of temperature, flow rate and purity.

Commitment To Quality

Eliminate defects and uniformity problems by using a particle-free, microdroplet-free water vapor source. Use precision-delivered pure water vapor to avoid costly scrap.

Introducing the RASIRC RainMaker® Humidification System

Precision Water Vapor Delivery System

For precise, pure water vapor delivery, choose the RainMaker Humidification System. Set your flow rate or dewpoint and the RHS delivers consistent oxide growth rates that are repeatable wafer-to-wafer, batch-to-batch, and furnace-to-furnace.

The RHS uses adaptive closed loop control to ensure repeatability. Process parameters are set through automated process recipes or touchscreen interface. Internal sensors for pressure, flow, and temperature trigger automatic adjustments to maintain the desired flow rate. A proprietary non-porous membrane within the RHS excludes particles, microdroplets, and volatile gases from entering the water vapor stream. 

Batch-to-Batch Repeatability

Fine-tuned instrument

  • The RHS precisely controls water vapor to within 2% of set point from batch-to-batch, unit-to-unit.
  • Control is consistent across the full RHS range of flow rates and dew points.  

Controlled Oxidation Rate

Consistent, particle-free delivery

  • The RHS maintains stability within 2% of the set point, ensuring that oxidation rate is constant and predictable.
  • Control is consistent across the full RHS range of carrier gas flow rates and dew points.

Damage-Free Oxidation

Tight water vapor control

  • Eliminates erratic oxidation through tight water vapor control
  • Filters out contaminants using a patented membrane
  • Tests show that the RHS delivers nearly zero droplets while competing flash vaporizers deliver high water droplet counts.

Better than Bubblers

Bubblers are inaccurate due to fluctuations in gas and liquid temperature, operating pressure, liquid level, and thermal droop. Contamination is left behind during vaporization and there is no mechanism to prevent the entrainment of dissolved gas, volatile molecular contaminants, and microdroplets that can carry particulate and ionic molecular contaminants.

Bubblers have very limited gas flow rates, because at higher rates violent boiling will throw liquid and particles into downstream piping. Spikes of moisture/water droplets are common during bubbler operation.

More Reliable than Flash Vaporizers

Vaporizers atomize water, combusting any small droplets into molecular water. The temperature of vaporization is very high, with heater transfer limited by carrier gas flow rate and heating elements.

In addition, water is aggressive and can corrode the vaporizer internal components, leading to long term stability and reliability issues. Vaporizer output is entrained with dissolved gas, micro-droplets, and particles.

Latest News

RainMaker Humidification System (RHS) Datasheet


The RHS purifies and precisely controls water vapor delivery, reducing costs, increasing yield and improving throughput. Delivery of water vapor can be controlled from low ppm levels to high concentrations.


RainMaker Humidification System for Precise Delivery of Water Vapor into Atmospheric and Vacuum Applications


Water vapor has multiple applications across industries including semiconductor, photovoltaic, fuel cells, carbon nanotubes, glass coating, and pharmaceuticals. Precise control of this water vapor is necessary to ensure that product yield and performance are consistent. In many of these applications, the process is performed in a vacuum.


Particle Generation by Incomplete Vaporization of Condensable Fluids and Particle Prevention by Membrane Pervaporation


A study was conducted to compare the relative particle/microdroplet generation of pervaporation versus a flash vaporizer in both continuous and intermittent flow conditions. This paper details that study and includes particle data when applied to ALD film growth in the appendix.


RASIRC products generate and deliver water vapor, hydrogen peroxide and hydrazine gas in controlled, repeatable concentrations to critical processes.


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