Vaporization of critical process chemistries is not an easy task. To begin with, advanced processes are constantly changing and using novel chemistries for which data may be limited. In some instances, researchers may need vaporization equipment for chemistries whose identities they don’t want to disclose. Once the chemical properties are determined, the job of balancing liquid flows, carrier gas flows, upstream and downstream pressures and materials compatibility can start. Often a carrier gas is required, and the carrier flow must be carefully calculated and controlled during process. The temperature of the vaporizers is also key – balancing the required temperature vs the potential to heat-induced damage to the liquid. The determination of the right vaporization method leads to the careful selection and specification of the supporting instruments – gas / liquid flow controllers / meters, vaporization nozzles and temperature controllers. Not an easy process but a process in which HORIBA is a global leader.
HORIBA has vaporization solutions ranging from fractional grams/minute to >25g/min. As a solutions provider, we can not only recommend vaporization components like our VC and MV series but we can also provide a fully integrated system like our LSC / LU. By using our world-leading gas and liquid mass flow controllers and meters in conjunction with our vaporizers, users are assured accurate and repeatable vaporization of critical process chemistries.
The graph above shows the different possible states of matter. There are two ways to get from a liquid to a gaseous state. The first method involves increasing the temperature while holding the pressure steady, as indicated by the arrow with the broken line . This method is commonly used in everyday settings—to boil water and convert it to steam, for example. Heating a liquid takes time, however, which makes rapid vaporization difficult. On the other hand, one can also heat the liquid in advance and then abruptly reduce the pressure, as illustrated by the arrow with the solid line . The pressure in the vaporization section of the injector can be reduced instantaneously, and this makes it possible to vaporize a liquid source instantaneously.
The following list covers the major steps involved in vaporizing a liquid source and supplying it to the process chamber.
The liquid source's flow rate is measured, and the amount of liquid is feedback controlled by the valve.
The liquid is instantaneously and completely vaporized.
Vaporization systems that use the injection method sequentially carry out steps 1, 2 and 3 listed above. The VC series units measure the liquid flow of the liquid source using a mass flow meter, and do not use a carrier gas. The MI/MV series units use a mass flow meter for measurement, and feature a mass flow controller that introduces a carrier gas into the unit to vaporize the liquid source.
This vaporization method is used in the MI/MV series. Since the pressure of the carrier gas is higher ahead of the nozzle inside the injector, it can be heated efficiently. The liquid source and the heated carrier gas are mixed together in the gas/liquid mixing area just before the nozzle, the pressure is reduced as they pass through the nozzle, which vaporizes the mixture.
Vaporization efficiency is higher than with traditional vaporization methods. When this method is used, larger flows can be generated, and the generation temperature can be reduced.
In semiconductor devices, which continue to require greater integration and detail, a variety of liquid sources are used to accentuate the characteristics of the films created. HORIBA STEC offers vaporization systems that are optimized to make the most of the characteristics of the various liquid sources used in today's cutting-edge processes.