Chamber pressure

About: Chamber pressure is a research topic. Over the lifetime, 2988 publications have been published within this topic receiving 30725 citations.

Silicon Carbide Epitaxy in a Vertical CVD Reactor: Experimental Results and Numerical Process Simulation

Abstract: In this paper an overview is given on the epitaxial growth of SiC in a vertical CVD reactor. Results concerning impurity incorporation and ways to achieve background doping levels as low as 10 14 cm -3 are discussed. Precise control of the C/Si ratio in the gas phase, which is easily achieved in the described reactor, and the use of reduced pressure, lead to good control of dopant incorporation over more than three orders of magnitude, and smooth surface morphology at growth rates higher than 5 μm/h. Doping variations < ±12% across 35 mm wafers can routinely be obtained. The quality of the epilayers is proven by electrical brakdown fields as high as 2 x 10 6 V/cm at N A - N D = 5 x 10 -15 cm -3 achieved in both pn and Schottky diodes and an electron mobility higher than 700 cm 2 /Vs at 300 K (4H-SiC) estimated from the on-resistance of these test devices. Another important experimental boundary condition, the influence of the gas composition at the end of the epitaxial growth process on the surface properties of the epitaxial layer, is described. It will be shown that surfaces nearly resistant against oxidation can be generated in a hydrogen free atmosphere. As a second main topic of this paper, results of an elaborate numerical process simulation will be described including both fluid mechanical and chemical behavior. The influence of the main process parameters like total flow, chamber pressure, and rotation speed on the stability of the flow was investigated. The results achieved are compared with experimental observations showing excellent agreement. The experimental observation of an irradiant layer in the gas phase in front of the wafer under typical process conditions is explained with the help of the numerical model. The usefulness of this specific feature for the optimization of process conditions is discussed.

Reactive ion etching of gallium nitride using hydrogen bromide plasmas

Abstract: The characteristics of the reactive ion etching (RIE) of gallium nitride (GaN) have been investigated using HBr, 1:1 HBr:Ar, and 1:1 HBr:H/sub 2/ plasmas. Etch rates were found to increase with plasma self-bias voltage for all gas mixtures exceeding 60 nm/min at -400 V for pure HBr. Higher etch rates were obtained for pure HBr than for HBr mixtures with Ar and H/sub 2/. Chamber pressure was also found to slightly affect etch rates for the pressure ranges investigated. The anisotropy of etched profiles was found to improve with increasing pressure. Smooth etched surfaces are also demonstrated. >

The Constant Volume Limit of Pulsed Propulsion for a Constant Gamma Ideal Gas

Abstract: The constant volume (CV) limit of pulsed propulsion was explored theoretically, where the combustion chamber was approximated as being time-varying but spatially uniform, while the nozzle flow was approximated as being one dimensional but quasi-steady. The CV limit was explored for the isentropic blow down of a constant y ideal gas for fixed expansion ratios and for variable expansion ratios which were adjusted to match the pressure ratio at all times. The CV limit calculations were notable in that all the fixed expansion ratio results could be expressed as analytical solutions. The CV limit was then compared with two relevant constant pressure (CP) cycles. Among the several conclusions were that using a fixed expansion ratio nozzle during a CV blow down did not exert more than a 3% performance penalty over using a variable expansion ratio nozzle as long as the fixed expansion ratio nozzle was optimized for the blow down. Another major conclusion was that, while the impulse produced by a CV device could significantly exceed that of a CP device operating at the fill pressure of the CV device at elevated ambient pressures (e.g. , I atm), the impulse produced by a CP device could actually exceed, albeit only slightly, the impulse produced by a CV device when the ambient pressure was near zero, such as would occur in the near vacuum conditions in space. Nomenclature A - area c - speed of sound CF - thrust coefficient cp - specific heat at constant pressure F - thrust g(Y) - eq. (4) / - impulse rate of mass flow Mach number velocity pressure

Pressure balanced inner chamber of a drilling head

Abstract: A system for maintaining an optimum pressure balance within an inner chamber of a drilling head for improved seal life and integrity. The system maintains a pressure differential across the seals thereby preventing well fluids from contaminating the seals and improving their useful life. The drive ring of a drilling head is rotatably supported by a series of bearings disposed within a bearing chamber. The secondary chamber of the drilling head is sealed to prevent contaminants from entering the chamber and fouling the seals. The seals withstand the borehole well pressures to prevent the introduction of contaminants, by maintaining a pressure differential across the seals. The present system compensates for variations in the borehole pressure. A pressure compensator is in communication with the borehole to activate a lubricant pump for increasing lubricant pressure within the inner chamber in response to increased borehole pressures. A relief valve associated with the inner chamber relieves pressure in the seal chamber to maintain lubricant pressure at optimum levels when borehole pressure decreases for controlled operation of the seals. Additional check valves are included in the inner chamber to control the chamber pressure while preventing contamination of the lubricant.