Interaction of Oxygen with Hot Tungsten

Abstract

The reaction of oxygen at a polycrystalline tungsten surface has been studied over a temperature range from 1300° to 2450°K and for oxygen pressures from ∼10−5 to ∼10−8 torr. A mass spectrometer was used to measure the oxygen pressure. In determining absolute pressures care was taken to avoid errors which may arise due to spurious currents in a Bayard—Alpert ion gauge. The efficiency of removal of carbon impurity from tungsten, by heating in oxygen, was determined. After obtaining a low carbon content, the rates of removal of oxygen at the tungsten surface were determined as a function of temperature. At temperatures below ∼2000°K evaporation of oxides of tungsten occurs at predictable rates. At higher temperatures atomic oxygen is produced and the observed rate of removal of oxygen is strongly influenced by the specific surfaces present in the entire system. For example, a silver surface efficiently reacts with oxygen atoms, without apparent saturation, to give a large apparent increase in the pumping speed at a tungsten surface enclosed in a glass system.

Practical guide to the use of Bayard–Alpert ionization gauges

“…21 Redhead also showed that the use of a simple modulator electrode in a Bayard-Alpert gauge can permit both the detection of such errors and their correction, 20 though in at least one instance modulator readings were only valid when the pressure reached a steady state. 10 In measurement of pressure changes, the data of Fig. 2 show the slow response to a pressure measured by the ion gauge as compared to the mass spectrometer, but good agreement at equilibrium.…”

“…As the temperature increases above ϳ1650 K atomic oxygen production starts and by 2000 K is the predominant species. 10 Atomic oxygen may recombine at surfaces within the system, resulting in no net pumping, but it is also very reactive and will react with some surfaces in the vacuum system, leading either to a pumping effect, or to the generation of gaseous impurities ͑which is discussed later͒. The effective pumping simply depends upon the materials present in a system.…”

“…In a glass system the atomic recombination is low so that atoms travel long distances. 10 In a metal system oxygen atoms may recombine at the wall more rapidly than in a glass system, and so result in less net pumping. The magnitude of pumping that will result from these various processes is clearly difficult to predict.…”

“…For example, a small UHV system achieved a pressure of ϳ1.5ϫ10 Ϫ10 Torr after an overnight bake at 400°C; the pressures of residual gases were: CO, 3ϫ10 Ϫ11 ; CO 2 , 3ϫ10 Ϫ11 ; H 2 , 8ϫ10 Ϫ11 ; and H 2 O, 6ϫ10 Ϫ12 ; Torr. 10 The system included a BA gauge 3. Measurement of pressure in hydrogen containing a low level of carbon monoxide.…”

Real-time etching monitor using argon quadrupole mass spectrometry for 100 nm class WSiN gate fabrication

“…These carbon species are emitted by the tungsten filament of the QMS. 16,17 We therefore have to consider the effect of C 2 O ϩ because we used a small amount of oxygen in the etching gas to reduce the etching rate of the SiO 2 mask. Figure 3 shows the intensities of the M /eϭ12, 28, 40, and 44 signals as a function of the oxygen concentration in SF 6 -O 2 with the plasma off.…”