Utah-94-721002-System-Manual.pdf - 第47页
System Manual lñÑçêÇ=få ëíêìãÉåíë=mä~ëã~=qÉÅÜåçäçÖó== mä~ëã~ä~ Ä póëíÉã=NMM THERMOCOUPLE CHAMBER BASE WA F E R CLAMP TA B L E DARK SP ACE SHIE LD TA B L E S U P P O R T TUBE O RING PUMPDO WN PIPE F LANG E FEEDTHROUGH COM…
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to the periphery of the wafer. Helium is the preferred gas, because it has a very good heat
transfer ability. The use of other gases is possible, preferably inert gases.
The supply of helium is fed by a pressure control device, which receives an analogue setpoint
from the machine’s control system. The pressure control device adjusts the gas flow through
itself to control the pressure at its output side. The pressure is controlled within the range 0
to 50 Torr. A pressure of greater than 20 Torr could damage very thin substrates.
If the wafer is clamped down successfully the chamber pressure will show a slight rise of a few
milliTorr when the helium is producing a pressure of 10 Torr on the wafer.
If there is a massive pressure rise and the Turbo Controller display shows a high load, then the
wafer is insufficiently clamped and in order to achieve the set pressure the controller is using
an excessive gas flow.
The helium pressure is released into the process chamber at the end of a process (using a
normally-open valve). This prevents the wafer moving when it is unclamped.
Tip: Finish a process with a ten-second pumping step without helium. This will
reduce wafer mishandling.
A flow meter in the helium supply also reads the gas flow necessary to maintain the pressure.
A typical process uses 5 - 20 sccm to maintain 10 -15 Torr behind the wafer.
Tip: Some wafers mate very well with the electrode top surface and use less than 2
sccm to maintain 10 Torr. This can give a control problem, with the helium
feeding in pulses. Roughening the aluminium electrode with an abrasive pad
can increase the helium flow by a few sccm and allow proper control.
Do not turn on the helium unless the wafer is clamped.
Description
UC Davis 94-721001 Issue 1: March 06 Page 3-10 of 22 Printed: 22-Mar-06, 7:29
System Manual lñÑçêÇ=fåëíêìãÉåíë=mä~ëã~=qÉÅÜåçäçÖó== mä~ëã~ä~Ä póëíÉã=NMM
THERMOCOUPLE
CHAMBER
BASE
WAFER
CLAMP
TABLE
DARK SPACE
SHIELD
TABLE SUPPORT
TUBE
O RING
PUMPDOWN
PIPE FLANGE
FEEDTHROUGH
COMPONENTS
STAINLESS
STEEL
BELLOWS
SPRING
COMPRESSED
AIR CYLINDER
COMPRESSED
AIR CYLINDER
(ONE EACH SIDE
OF CLAMPING
PLATE)
WAFER
LIFT
ASSEMBLY
(FITS INSIDE
TABLE SUPPORT
TUBE)
Clamping
plate
Clamping
ring
Setscrew &
compression
spring (3-off
on each side
of clamping
ring)
3-pin wafer
support
Quartz
insert
SAFETY RELIEF
VALVE
CONTROL VALVE
LIQUID NITROGEN
IN
LIQUID NITROGEN
OUT
HELIUM IN
Fig 3.3: 94-100-5-12A Cryo / heated -150 / 400C He lower electrode
Description
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This kit comprises a 500W RF Generator and an OIPT Automatch Unit.
The RF generator produces a 13.56MHz output, which is fed via the automatch unit to the
lower electrode to produce the plasma. The automatch unit adjusts the impedance of its
output to match the impedance of the lower electrode to ensure maximum power transfer.
For details of these units, refer to the manufacturer’s literature in Volume 3 of this manual.
The automatch unit can be manually adjusted if necessary, see Operator Adjustments in
Section 5 of this manual.
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The inductively coupled plasma source is 180mm in diameter, which gives uniformity suitable
for use with wafers up to four inches in diameter. An RF generator (3kW 13.56MHz) and
automatch unit are included. A quartz or alumina discharge chamber is supplied, according to
the process specification. For full details of this source, refer to the ICP 180 manual (provided
as a supplement to this manual – refer to the contents list).
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The vacuum system is shown in Fig 3.4.
The process chamber is pumped by an Alcatel ATP900 turbomolecular pump via an Automatic
Pressure Controller (APC). The turbomolecular pump is backed via an isolation valve by an
Alcatel 2063 C2 rotary vane pump.
The process chamber process pressure is measured by a temperature compensated 100-mTorr
Capacitance Manometer gauge. Note that the CM gauge output does not stabilise until it has
been switched on and under vacuum for 15 minutes.
Base pressure is measured by an active Penning gauge, which is disabled at pressures above
10 mTorr.
A Vacuum Switch monitors the chamber pressure. When the pressure falls below 600 mbar, its
contacts close to enable the 24V process line and allow the process gases and the RF to
operate.
The automatic load lock is pumped by an Alcatel 2015 C2 rotary vane pump. A Pirani gauge
measures pressure.
For details of the vacuum pumps and gauges, refer to the manufacturer’s literature in Volume
3 of this manual.
Description
UC Davis 94-721001 Issue 1: March 06 Page 3-12 of 22 Printed: 22-Mar-06, 7:29