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Vacuum measurements in small sealed systems
Abstracts changcohcr has occurred because of the significant pcrformancc advantages of low pressure CVD (LPCVD) systems compared with atmospheric pressure systems. In this presentation we shall illustrate these trends by’refcrence to the deposition of layers such as epitaxial silicon. doped polysilicon and tungsten. and we shall discuss the ways in which growth conditions in the reactor and. particularly, the chemistry of the CVD process can affect growth rate. uniformity. composition, structure and electrical propcrtics.
Computer
supported
design of vacuum systems:
calculation
of
pumping speed and simulation of pump down Leyhold
Th Gebele, W Buschbeck and W Schwarz,
AC, PO Box
1555. D-6450 Hunri~. FRG
Today’s design and optimization of complex vacuum systems requires the computer supported simulation of vacuum pump sets and pump down curves. Such a program contains calculation modules for all types of pumps like forepumps. Roots blowers, turbomolecular, diffLlsion and cryopumps. Also pressure dependent conductances between adjacent pump stages and between the pump set and the vacuum chamber have to be taken into consideration. In order to increase the pumping speed for water vapour, vacuum chambcrs arc often equipped with cryosurfaces. Their pumping speeds have to be calculated pressure and temperature dependent. For the computation of the pressure-time curve of a chamber in the high vacuum range, the precise simulation of desorption and its specific time dependence are essential. This paper describes the foundations of a simulation program and shows some calculated examples.
indium surface described by the process 31nZO(G) is examined, too.
In,O,(S)+4In(L)
+
Vacuum measurements in small sealed systems
J Retina,
M
Zumer
and B Erjavec,
r~ukcrunzsko tehniko, Ljuhijma.
InStitut x
&ktroniko
in
Yugol.\aritr
Single cell sputter-ion pumps are often used for appendage pumping of small sealed systems such as electron tubes. After evacuation and pinching-off. the ion pump provides additional gas clean-up and thus extends the lifetime of the tube. Below IO-’ Pa the discharge is magnetically confined and the current drawn by the sputter-ion pump is linearly proportional to the pressure. This phenomenon enables the use of the sputterion pump as a pressure gauge over a part of its operating range. Below IO-’ Pa the use of the pump as a gauge is limited due to the field emission and the insulator leakage currents. The latter overshadow the current drawn by the discharge at low pressures. Discharge ignition is yet another difficulty at low pressure use of the sputter-ion pumps. Single cell sputter-ion pumps, which are available on the market, hardly start below IO- ’ Pa. In the electron tubes evacuated in our laboratory the pressure after pinch-off is below the striking pressure of appendage pumps. This problem is overcome by inserting hot cathodes in single cell sputter-ion pumps and by improving the insulation in order to minimize leakage currents. Modified ion pumps start and work at discharge currents below IO-“’ A and indicate pressures below IO-* Pa. Thus the monitoring of the vacuum in the electron tubes is possible after processing. The influence of diKerent operating conditions on further degassing of the electron tube elements can be evaluated.
-__ AES studies of surface phenomena on liquid indium solder M
Jenko,
c~ectroniko
E Kansky, in ukuutnsko
B Erjavec tehniko,
and
B PraTek,
Ljubljnnn,
ItzStitut :(I
Yugos[ucia
FILIXICSSvacuum soldering is widely used for hermetical encapsulation of second and third generation image intensifier tubes. Extremely clean surFaces are indispensable for obtaining good wetting at soldering processes of this sophisticated sealing technique. Nonwetting or leakage of fluxless vacuum soldered seals may often be caused by a thin oxide film, covering the liquid solder. The solder is usually a tow melting indium alloy or pure indium. ItI Jitrt surface analytical investigation of these complex surface phenomena with AES is accomplished. An AES spectrometer is adapted to study the following phenomena :
(a) oxidation of solid and liquid indium in the tcmpcraturc range 20 C < T< 400 C. in vacuum at 5 x lo-’ Pa oxygen pressure ; (b) cleaning processes of thin oxide InZO, film on liquid indium surface in the temperature range 20°C < T d 300°C in UHV; and (c) isothcrmul dissociation of thin oxide In201 film on liquid 946
Ion plated aluminium on carbon fibres N A G Ahmed, Hudders$eld Enginerring
Polytechttic,
Depurttwen~, Queensgutr.
Electrirxl
mti Elwrrottic~
Huddersfield,
HDl
3DH,
UK
In recent years there have been many research and development investigations on carbon fibres for military and civilian applications. The fact that carbon fibres have very good strength to weight properties has made them attractive to the aircraft industry and at present fibre/epoxy composites are being used for the skin of the high performance AV-8B and F-18 aircrafts. However, the poor electrical conductivity of the fibres represent a real problem, particularly where electromagnetic interference (EMI) shielding by the composite aircraft skin is important. WC report here preliminary results of using ion plating techniques to deposit thick and adherent aluminium coating on carbon fibres with good electrical conductivity. By controlling the process parameters such as substrate bias and current density, an adherent aluminium coating of IO pm thickness was successfully deposited on carbon fibres. Samples as large as 30 x 3 cm were ion plated with good uniformity.
Computer
supported
design of vacuum systems:
calculation
of
pumping speed and simulation of pump down Leyhold
Th Gebele, W Buschbeck and W Schwarz,
AC, PO Box
1555. D-6450 Hunri~. FRG
Today’s design and optimization of complex vacuum systems requires the computer supported simulation of vacuum pump sets and pump down curves. Such a program contains calculation modules for all types of pumps like forepumps. Roots blowers, turbomolecular, diffLlsion and cryopumps. Also pressure dependent conductances between adjacent pump stages and between the pump set and the vacuum chamber have to be taken into consideration. In order to increase the pumping speed for water vapour, vacuum chambcrs arc often equipped with cryosurfaces. Their pumping speeds have to be calculated pressure and temperature dependent. For the computation of the pressure-time curve of a chamber in the high vacuum range, the precise simulation of desorption and its specific time dependence are essential. This paper describes the foundations of a simulation program and shows some calculated examples.
indium surface described by the process 31nZO(G) is examined, too.
In,O,(S)+4In(L)
+
Vacuum measurements in small sealed systems
J Retina,
M
Zumer
and B Erjavec,
r~ukcrunzsko tehniko, Ljuhijma.
InStitut x
&ktroniko
in
Yugol.\aritr
Single cell sputter-ion pumps are often used for appendage pumping of small sealed systems such as electron tubes. After evacuation and pinching-off. the ion pump provides additional gas clean-up and thus extends the lifetime of the tube. Below IO-’ Pa the discharge is magnetically confined and the current drawn by the sputter-ion pump is linearly proportional to the pressure. This phenomenon enables the use of the sputterion pump as a pressure gauge over a part of its operating range. Below IO-’ Pa the use of the pump as a gauge is limited due to the field emission and the insulator leakage currents. The latter overshadow the current drawn by the discharge at low pressures. Discharge ignition is yet another difficulty at low pressure use of the sputter-ion pumps. Single cell sputter-ion pumps, which are available on the market, hardly start below IO- ’ Pa. In the electron tubes evacuated in our laboratory the pressure after pinch-off is below the striking pressure of appendage pumps. This problem is overcome by inserting hot cathodes in single cell sputter-ion pumps and by improving the insulation in order to minimize leakage currents. Modified ion pumps start and work at discharge currents below IO-“’ A and indicate pressures below IO-* Pa. Thus the monitoring of the vacuum in the electron tubes is possible after processing. The influence of diKerent operating conditions on further degassing of the electron tube elements can be evaluated.
-__ AES studies of surface phenomena on liquid indium solder M
Jenko,
c~ectroniko
E Kansky, in ukuutnsko
B Erjavec tehniko,
and
B PraTek,
Ljubljnnn,
ItzStitut :(I
Yugos[ucia
FILIXICSSvacuum soldering is widely used for hermetical encapsulation of second and third generation image intensifier tubes. Extremely clean surFaces are indispensable for obtaining good wetting at soldering processes of this sophisticated sealing technique. Nonwetting or leakage of fluxless vacuum soldered seals may often be caused by a thin oxide film, covering the liquid solder. The solder is usually a tow melting indium alloy or pure indium. ItI Jitrt surface analytical investigation of these complex surface phenomena with AES is accomplished. An AES spectrometer is adapted to study the following phenomena :
(a) oxidation of solid and liquid indium in the tcmpcraturc range 20 C < T< 400 C. in vacuum at 5 x lo-’ Pa oxygen pressure ; (b) cleaning processes of thin oxide InZO, film on liquid indium surface in the temperature range 20°C < T d 300°C in UHV; and (c) isothcrmul dissociation of thin oxide In201 film on liquid 946
Ion plated aluminium on carbon fibres N A G Ahmed, Hudders$eld Enginerring
Polytechttic,
Depurttwen~, Queensgutr.
Electrirxl
mti Elwrrottic~
Huddersfield,
HDl
3DH,
UK
In recent years there have been many research and development investigations on carbon fibres for military and civilian applications. The fact that carbon fibres have very good strength to weight properties has made them attractive to the aircraft industry and at present fibre/epoxy composites are being used for the skin of the high performance AV-8B and F-18 aircrafts. However, the poor electrical conductivity of the fibres represent a real problem, particularly where electromagnetic interference (EMI) shielding by the composite aircraft skin is important. WC report here preliminary results of using ion plating techniques to deposit thick and adherent aluminium coating on carbon fibres with good electrical conductivity. By controlling the process parameters such as substrate bias and current density, an adherent aluminium coating of IO pm thickness was successfully deposited on carbon fibres. Samples as large as 30 x 3 cm were ion plated with good uniformity.