Mark W. Raynor

Techniques for the measurement of trace moisture in high-purity electronic specialty gases

The control of water vapor (moisture) contamination in process gases is critical to the successful manufacture of semiconductor devices. As specified moisture levels have become more stringent, there is a growing demand for more sensitive analytical methods. Instrumental methods currently being used or in development for measuring trace moisture at ppbv levels include Fourier transform infrared spectroscopy, tunable diode laser absorption spectroscopy, cavity ringdown spectroscopy, intracavity laser spectroscopy, electron impact ionization mass spectrometry, and atmospheric pressure ionization mass spectrometry. In addition, sensor-based technologies such as oscillating quartz crystal microbalances, and chilled mirror-, capacitor-, and electrolytic-based hygrometers operate in this regime. These approaches are presented and reviewed. As the success of each trace moisture method is dependent on the degree to which the different process gases interfere with the measurement process, important process gas app...

Contamination control in gas delivery systems for MOCVD

Each of the elements of a gas distribution system potentially is a source of contamination in film growth reactors. A detailed technical understanding of the origin and properties of the most common contaminants, their fluctuations and their interaction with the different elements in the delivery system are essential to provide consistent high gas purity for device growth. Governing processes in the gas source, the delivery system, and purifiers were addressed with selected examples, along with approaches for integrated solutions. The examples include impurity fluctuation in NH3 as a function of the method of delivery, moisture outgassing from particle filters as a function of filter material and matrix gas, and low-level breakthrough in packed bed adsorbent-based purifiers as a result of transport and reaction rate limitations.

Cylinder Materials of Construction for Ultra-High Purity HBr in Advanced Semiconductor Etch Processes

Anhydrous HBr used in etch processing for the semiconductor industry requires strict impurity control. However, the gas cylinder material of construction plays a critical role in controlling and maintaining purity levels of the delivered HBr process gas and must be carefully selected. In this work Ni-lined AISI 4130 Cr-Mo steel cylinders are compared against the gas industry standard AISI 4130 Cr-Mo steel cylinders with regard to (a) surface roughness/area and oxide layer thickness after exposure to HBr and (b) the concentration of moisture in delivered HBr gas. Over the period of a year, the surface roughness increase of the polished Cr-Mo steel package doubles that of the Ni-lined package and the penetration of the oxide layer into the metal for the Cr-Mo steel is over 10 times that for the Ni surface. Finally the more inert surface of the Ni lining is shown to lower the moisture concentration in the HBr gas by ~4 times. These findings demonstrate that Ni-lined AISI 4130 Cr-Mo steel provides a superior package for Ultra High Purity HBr storage and delivery.

Trace moisture emissions from heated metal surfaces in hydrogen service

The formation of trace moisture by exposure of dry heated surfaces of 316 L stainless-steel, Restek Silcosteel®, and nickel 1/8 in. outer diameter line segments to purified Ar and H2 was studied using atmospheric pressure ionization mass spectrometry at flow rates of 2 slpm. Prior to H2 exposure, adsorbed moisture was removed by heating incrementally to 500 °C in an argon matrix, where the Restek Silcosteel® material released a maximum of 50 ppb moisture at 300 °C and moisture spikes from the Ni and stainless-steel surfaces reached several 100 ppb. Upon exposure to H2, persistent low ppb moisture emissions due to the reduction of surface oxide species were observed at temperatures as low as 100 °C. Spikes at 300–500 °C ranged from ∼100 ppb for the stainless-steel lines to 400 ppb for the Restek Silcosteel® material. The observed moisture emissions have to be considered as a potential contamination source for high-purity processes utilizing H2 purge at elevated temperatures.

Optimization of palladium cell for reliable purification of hydrogen in MOCVD

The reliability of a newly engineered palladium membrane diffuser for hydrogen purification has been investigated. The purifier was exposed to operating conditions that cause high failure rates in other currently available commercial designs. Stress tests include repeated power outages, and rapidly increasing and decreasing flow rates. Helium leak tests confirmed that the membranes maintained their integrity under these conditions. Atmospheric pressure ionization mass spectrometry (APIMS) verified sub-ppb efficiency of the purifier for impurity removal. Flow rate measurements as a function of pressure gradient and membrane temperature indicated that the flux across the membrane was not limited by external mass transfer resistance and followed basic laws of diffusion.