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A simple mass spectrometer for the analysis of argon at ultra-high vacuum
Classified a b s t r a c t s 126--135 840-930 A. Results of the rotational and vibrational analyses for the B'-x, B"-x, D-x and D'-x bands are given. The perturbation parameters between the various B and D states have been estimated in each case. T Namioka, J Chem Phys, 41 (7), Oct 1964, 2141-2153. 19 : 41 126. Measurement of layer thickness of silicon epitaxial wafers.
(USA) Modern non-destructive methods based on infrared reflectance measurements are described and their advantages and limitation discussed. R J Walsh, Semiconductor Prod Solid State Technol, 7 (8), Aug
1964, 23-27. 19 : 41 127. Ultrahigh vacuum measurements of the optical properties of copper. (USA) A n ultrahigh vacuum system is described in which films can be evaporated and their optical properties examined in situ. Samples kept at 10 -8 torr showed a sharp decrease in the dielectric constant during the first 5 hours after deposition. Sample kept at 10 -5 torr showed~no variation with time. W T Spencer and M P Givens, J Opt Soc Amer, 54 (11), Nov 1964,
1337-1340.
II. Vacuum apparatus and auxiliaries 20.
Pumping systems
20 128. General purpose metallurgical vacuum system. (USA) The system is built around a cold wall vacuum chamber, 18 in. diameter by 22 in. in length which can accommodate a variety of accessories to perform such operations as high temperature resistance heating, arc melting and casting, induction melting and casting, inert atmosphere and manual dry box operation. Some of the specific processing operations which can be performed includes the following: Making atmosphere or moisture sensitive powdered metal preparations. Sintering in vacuum up to 3000°C. Melting or alloying and tilt pouring sufficient quantities of metal to allow preparing of test specimen. Vacuum brazing etc. (USA) Anon, Res & Develop, 15 (12), Dec 1964, 50-51.
21. Pumps and pump fluids 21 : 41 129. Low temperature titanium evaporation pump of large output.
(France) A titanium evaporation pump with an active surface of 12,000 cmz at liquid nitrogen temperature is described. The pump is backed with an oil diffusion pump of 60 cm diameter. The maximum sticking probability is a b o u t 0.9 for air and 0.3 for hydrogen, giving pumping speeds of approx. 130,000 L/see and 150,000 L/see respectively. These values are reduced to 30,000 l./sec and 75,000 l./sec by conductance losses at pump entry. Pressures as low as 10 -a torr can be maintained in unbaked systems by the use of titanium pumps, whilst lower pressures of the order of 10-1° torr are possible if some trouble is taken. The main drawback of these pumps is their selectivity in handling gases. Removal of deposits and ieplacement of filaments is only required after relatively long intervals of operation. (France) F Prevot and Z Sledziewski, Le Vide, 19 (113), Sept~Oct 1964,
342-349. 21 130. Study on the contamination by oil vapour of a standard vacuum installation. (France) Contamination in a standard vacuum system by oil vapour was estimated by measuring the thickness of SiC film deposited on a clean silica crystal kept at 1000 °C inside the recipient. The film was measured by electron diffraction. The system under test consisted of a two-stage vane pump followed by an oil diffusion pump. The usual n u m b e r of traps and baffles was provided. The tests show that the residual contamination is entirely due to oil vapour emanating from the primary vane pump. The passage of this vapour can be
restricted by reducing the conductance of the primary inlet, i.e. increasing the pressure at the diffusion pump exit. This reduces the free path of the oil molecules and thus increases their chance of being trapped before entering the secondary pump. (France) G Blet and O Coudeyras, Le Vide, 19 (112), July~Aug 1964,
233-238. 21 131. Theoretical investigation of oil back streaming through a vacuum pump. (USA) A n approximate theoretical analysis of the oil backstreaming through an optically tight, liquid nitrogen cooled elbow trap is made. Sticking coefficient, oil deflection due to intermolecular collision and diffusion are considered and numerical results are presented for the back streaming through a 36 in. diameter trap. The r6sults are discussed from the standpoint of ultrahigh vacuum system operation procedures and trap design in general. The advantages of double-bounce traps, dual dimensional traps and the use of low pressure purge gas are pointed out. (USA) D W Jones and C A Tsonis, J Vac Sci and Techn, 1 (1), Sept~Oct
1964, 19-22. 21 132. Method of obtaining oil-free vacuum with oil diffusion pumps.
(USA) The density of the pump fluid vapour backstreaming into the high vacuum space is so low above a plane running through the edge of the uppermost nozzle of a diffusion pump, that molecular collisions can be neglected and a straight line movement in the upward direction must exist. To study this motion, the author has developed a pin hole camera consisting of a thin copper foil with a 1 m m pinhole and a collector plate consisting of an incomplete Fabry-Perrot interference filter. The camera is placed vertically above the uppermost nozzle hood. After exposure, the filter was completed by vacuum deposition of the missing films. At all places on which fluid molecules had been precipitated, the thickness of the film had been changed and the resultant change in colour allowed conclusions to be drawn concerning the intensity and distribution of the sources responsible for backstreaming. As a result, an improved form of baffle was developed, incorporating a water-cooled cowl over the upper nozzle and additional condenser plates. (Liechten-
stein) O Winkler, Res & Develop, 15 (10), Oct 1964, 58-64. 21 133. Hydrocarbon formation in ion pumps. (USA) Some, if not all, of the hydrocarbons observed emanating from an ion pump are synthesized from the hydrogen and carbon containing molecules (not necessarily hydrocarbons) being pumped. It is useful to be aware of the reactions occurring in the pump and to consider the effect of these reactions on the experiments being performed.
( USA ) D Lichtman, J Vac Soc & Techn, 1 (1), Sept~Oct 1964, 23-24.
22. Gauges 22 The study of the chemisorption of hydrogen on polycrystailine tungsten filaments by the flash method using a pulse mass spectrometer. See abstract n u m b e r i 13. 22 Residual argon partial pressure changes due to an intermittently operated Bayard-Alpert ionization gauge in ultrahigh vacuum. See abstract number 198. 22 134. A simple mass spectrometer for the analysis of argon at ultrahigh vacuum. (Great Britain) E Furrar et al, Nature, "204 (4958), 7 Nov 1964, 531-533. 22 : 42 135. Measurements with a modulated Bayard-Alpert gauge in alumino-silicate glass at pressures below 10 -1~ torr. (USA) The background conditions achieved in a simple ultrahigh vacuum system with an envelope of alumino-silicate glass (Corning 1720) have been studied. Pressures were measured by a dynamic method and also with a modulated Bayard-Alpert gauge. G o o d agreement between the two methods was obtained using a modified analysis for the modulated gauge. A total pressure of 8 × 10 -la torr (equivalent nitrogen) was measured with the whole system at r o o m temperature, and one of 7 × 10 -15 torr (equivalent nitrogen) was 83
(USA) Modern non-destructive methods based on infrared reflectance measurements are described and their advantages and limitation discussed. R J Walsh, Semiconductor Prod Solid State Technol, 7 (8), Aug
1964, 23-27. 19 : 41 127. Ultrahigh vacuum measurements of the optical properties of copper. (USA) A n ultrahigh vacuum system is described in which films can be evaporated and their optical properties examined in situ. Samples kept at 10 -8 torr showed a sharp decrease in the dielectric constant during the first 5 hours after deposition. Sample kept at 10 -5 torr showed~no variation with time. W T Spencer and M P Givens, J Opt Soc Amer, 54 (11), Nov 1964,
1337-1340.
II. Vacuum apparatus and auxiliaries 20.
Pumping systems
20 128. General purpose metallurgical vacuum system. (USA) The system is built around a cold wall vacuum chamber, 18 in. diameter by 22 in. in length which can accommodate a variety of accessories to perform such operations as high temperature resistance heating, arc melting and casting, induction melting and casting, inert atmosphere and manual dry box operation. Some of the specific processing operations which can be performed includes the following: Making atmosphere or moisture sensitive powdered metal preparations. Sintering in vacuum up to 3000°C. Melting or alloying and tilt pouring sufficient quantities of metal to allow preparing of test specimen. Vacuum brazing etc. (USA) Anon, Res & Develop, 15 (12), Dec 1964, 50-51.
21. Pumps and pump fluids 21 : 41 129. Low temperature titanium evaporation pump of large output.
(France) A titanium evaporation pump with an active surface of 12,000 cmz at liquid nitrogen temperature is described. The pump is backed with an oil diffusion pump of 60 cm diameter. The maximum sticking probability is a b o u t 0.9 for air and 0.3 for hydrogen, giving pumping speeds of approx. 130,000 L/see and 150,000 L/see respectively. These values are reduced to 30,000 l./sec and 75,000 l./sec by conductance losses at pump entry. Pressures as low as 10 -a torr can be maintained in unbaked systems by the use of titanium pumps, whilst lower pressures of the order of 10-1° torr are possible if some trouble is taken. The main drawback of these pumps is their selectivity in handling gases. Removal of deposits and ieplacement of filaments is only required after relatively long intervals of operation. (France) F Prevot and Z Sledziewski, Le Vide, 19 (113), Sept~Oct 1964,
342-349. 21 130. Study on the contamination by oil vapour of a standard vacuum installation. (France) Contamination in a standard vacuum system by oil vapour was estimated by measuring the thickness of SiC film deposited on a clean silica crystal kept at 1000 °C inside the recipient. The film was measured by electron diffraction. The system under test consisted of a two-stage vane pump followed by an oil diffusion pump. The usual n u m b e r of traps and baffles was provided. The tests show that the residual contamination is entirely due to oil vapour emanating from the primary vane pump. The passage of this vapour can be
restricted by reducing the conductance of the primary inlet, i.e. increasing the pressure at the diffusion pump exit. This reduces the free path of the oil molecules and thus increases their chance of being trapped before entering the secondary pump. (France) G Blet and O Coudeyras, Le Vide, 19 (112), July~Aug 1964,
233-238. 21 131. Theoretical investigation of oil back streaming through a vacuum pump. (USA) A n approximate theoretical analysis of the oil backstreaming through an optically tight, liquid nitrogen cooled elbow trap is made. Sticking coefficient, oil deflection due to intermolecular collision and diffusion are considered and numerical results are presented for the back streaming through a 36 in. diameter trap. The r6sults are discussed from the standpoint of ultrahigh vacuum system operation procedures and trap design in general. The advantages of double-bounce traps, dual dimensional traps and the use of low pressure purge gas are pointed out. (USA) D W Jones and C A Tsonis, J Vac Sci and Techn, 1 (1), Sept~Oct
1964, 19-22. 21 132. Method of obtaining oil-free vacuum with oil diffusion pumps.
(USA) The density of the pump fluid vapour backstreaming into the high vacuum space is so low above a plane running through the edge of the uppermost nozzle of a diffusion pump, that molecular collisions can be neglected and a straight line movement in the upward direction must exist. To study this motion, the author has developed a pin hole camera consisting of a thin copper foil with a 1 m m pinhole and a collector plate consisting of an incomplete Fabry-Perrot interference filter. The camera is placed vertically above the uppermost nozzle hood. After exposure, the filter was completed by vacuum deposition of the missing films. At all places on which fluid molecules had been precipitated, the thickness of the film had been changed and the resultant change in colour allowed conclusions to be drawn concerning the intensity and distribution of the sources responsible for backstreaming. As a result, an improved form of baffle was developed, incorporating a water-cooled cowl over the upper nozzle and additional condenser plates. (Liechten-
stein) O Winkler, Res & Develop, 15 (10), Oct 1964, 58-64. 21 133. Hydrocarbon formation in ion pumps. (USA) Some, if not all, of the hydrocarbons observed emanating from an ion pump are synthesized from the hydrogen and carbon containing molecules (not necessarily hydrocarbons) being pumped. It is useful to be aware of the reactions occurring in the pump and to consider the effect of these reactions on the experiments being performed.
( USA ) D Lichtman, J Vac Soc & Techn, 1 (1), Sept~Oct 1964, 23-24.
22. Gauges 22 The study of the chemisorption of hydrogen on polycrystailine tungsten filaments by the flash method using a pulse mass spectrometer. See abstract n u m b e r i 13. 22 Residual argon partial pressure changes due to an intermittently operated Bayard-Alpert ionization gauge in ultrahigh vacuum. See abstract number 198. 22 134. A simple mass spectrometer for the analysis of argon at ultrahigh vacuum. (Great Britain) E Furrar et al, Nature, "204 (4958), 7 Nov 1964, 531-533. 22 : 42 135. Measurements with a modulated Bayard-Alpert gauge in alumino-silicate glass at pressures below 10 -1~ torr. (USA) The background conditions achieved in a simple ultrahigh vacuum system with an envelope of alumino-silicate glass (Corning 1720) have been studied. Pressures were measured by a dynamic method and also with a modulated Bayard-Alpert gauge. G o o d agreement between the two methods was obtained using a modified analysis for the modulated gauge. A total pressure of 8 × 10 -la torr (equivalent nitrogen) was measured with the whole system at r o o m temperature, and one of 7 × 10 -15 torr (equivalent nitrogen) was 83