Hans H. Funke

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.

Detection of Trace Water Vapor in High-Purity Phosphine Using Cavity Ring-Down Spectroscopy

The presence of trace water vapor in process gases such as phosphine, used for compound semiconductor epitaxial growth, can negatively affect the optical and electrical properties of the final device. Therefore, sensitive H2O measurement techniques are required to monitor precursor purity and detect unacceptable contamination levels. A commercial cavity ring-down spectrometer that monitors an H2O absorption line at a wavelength of 1392.53 nm was investigated for service in high purity PH3. Spectral parameters such as the line shape of water vapor in the presence of PH3 as well as background features due to PH3 were measured at different pressures and incorporated into the data analysis software for accurate moisture readings. Test concentrations generated with a diffusion vial-based H2O source and dilution manifold were used to verify instrument accuracy, sensitivity, linearity, and response time. H2O readings at 13.2 kPa corresponded well to added concentrations (slope = 0.990 ± 0.01) and were linear in the tested range (0–52.7 nmol mol−1). The analyzer was sensitive to changes in H2O concentration of 1.3 nmol mol−1 based on 3σ of the calibration curve intercept for a weighted linear fit. Local PH3 absorption features that could not be distinguished from the H2O line were present in the purified PH3 spectra and resulted in an additional systematic uncertainty of 9.0 nmol mol−1. Equilibration to changing H2O levels at a flow rate of 80 std cm3 min−1 PH3 occurred in 10–30 minutes. The results indicate that cavity ring-down spectroscopy (CRDS) at 1392.53 nm may be useful for applications such as on-line monitoring (and dry-down) of phosphine gas delivery lines or the quality control of cylinder sources.

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.