Utah-94-721002-System-Manual.pdf - 第233页

System Manual lñÑçêÇ= fåëíêìãÉ åíë=m ä~ëã~ = qÉÅÜåçäçÖó== lfmq=póëíÉãë SKNKO= fåëí~ää~íáçå=çÑ=äçï=î~éçì ê=éêÉëëìêÉ=Ö~ëÉë=EÉKÖK=pá`ä Q I=_`ä P I=` Q c U F= The low vapour pressure can lead to condensation in the gas suppl…

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REGULATOR 0.5 BAR TO 5 BAR

(7 TO 75 PSIG) LOCATED

ADJACENT TO THE SYSTEM

SUPPLY TO

GAS POD

OR INTERNAL

GAS LINE

MINIMUM PRESSURE

3 BAR (45 PSIG)

ALL FITTINGS,

REGULATOR AND

FILTER TO BE

SEMICONDUCTOR

GRADE

LL TUBING TO BE

ELECTROPOLISHED

STAINLESS STEEL

NOTES:

Fig 6.1: Recommended process gas supply installation

Semiconductor grade fittings and pressure regulators, together with electropolished stainless

steel tube must be used to ensure that gas quality is not degraded.

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• Pipework fittings and pressure

regulators:

Semiconductor grade

• Gas handling tubing: Electropolished stainless steel

• Purity: At least 99.99% or higher to satisfy

process requirements.

• Filtration: A 2-micron filter is fitted to each

gas line supplied as part of the

system. For other grades of filter,

please consult OIPT.

• Regulation: 0.5 to 5 bar (7.5 to 75 psig)

• Minimum pressure at input to system: 2 bar (30 psig)

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The specifications for the Helium gas supply are as for those of the process gases given in sub-

sections 6 and 6.1 with the exception that the maximum pressure at the inlet to the

pressure controller must not exceed 3.5 bar (43 psig). The design of the Helium

pressure controller is such that it can be destroyed by higher pressures.

Services Specifications

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The low vapour pressure can lead to condensation in the gas supply lines, particularly at cold

points or when the gas passes into a cooler region. This condensation can result in a build up

of liquid in the gas pipe, usually at the low points or u-bends in the gas line, often leading to

instability of gas flow, especially if liquid condenses or flows into the MFC.

The low vapour pressure can also result in very low gas pressure if the gas cylinder is very

cold, e.g. if it is kept outdoors in the winter.

Therefore, it is important to adhere to the following guidelines:

(A) It is necessary to keep the gas cylinder indoors (in an extracted gas cabinet) to avoid

loss of line pressure when the outside temperature is cold.

However, do

NOT heat the gas cylinder with a heated jacket as this can cause

condensation problems when the gas passes into the cooler gas lines. Room

temperature is warm enough to provide sufficient vapour pressure.

(B) It is important to maintain a positive temperature gradient from the cylinder to the

MFC, or at least keep them at the same temperature. The simplest method is to

position the gas cabinet close to the gas pod, minimising the chances of temperature

differences, reducing the length of the gas pipe, and hence minimising the chances

of condensation. If this is not possible, then it is necessary to heat the gas lines by

the use of heater tape.

The MFC will also need to be heated. OIPT offers a heated MFC kit for these gases.

Alternatively, heater tape can be wrapped around the MFC. However, in this case, it

may also be necessary to detach the MFC from the backing plate to avoid heat loss

through the plate, and to cover the MFC in insulation material to avoid cooling from

air flow within the gas pod (from the gas pod exhaust).

It will then be necessary to set the MFC temperature hotter than the gas line

temperature, which in turn is hotter than the gas cylinder temperature. A typical set-

up might be MFC 40 °C or above, gas line 30-40 °C, and gas cylinder at room

temperature.

lines completely, and optimise the heater tape arrangement and temperature

setpoints before refilling the gas line.

(D) For SiCl

it is important to use a dedicated SiCl

MFC as this is designed specifically for

low-pressure condensable SiCl

operation.

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WARNING

IF LIQUID NITROGEN FACILITIES ARE NOT INSTALLED, OPERATED AND MAINTAINED

CORRECTLY, DANGEROUS SITUATIONS CAN RESULT. THESE INTRODUCE RISKS OF:

A) HAZARDOUS PRESSURE BUILD-UP CAUSED BY THE BOIL-OFF OF LIQUID

NITROGEN, WHICH CAN RESULT IN AN EXPLOSION.

B) PERSONAL INJURY FROM TOUCHING PIPEWORK OR OTHER SYSTEM

COMPONENTS CARRYING LIQUID NITROGEN. THIS RISK CAN REMAIN EVEN

AFTER VENTING THE CHAMBER.

C) ASPHYXIATION CAUSED BY THE BOILED-OFF LIQUID NITROGEN REPLACING

OXYGEN IN THE SYSTEM ENVIRONMENT.

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• Ensure that the Liquid Nitrogen installation is carried out in accordance with

local safety regulations. This includes the following:

(a) No part of the Liquid Nitrogen circuit can become blocked with ice

or other contaminants.

(b) Adequate precautions, e.g. pressure relief valves, are fitted to

prevent hazardous pressure build-up from boil-off of the Liquid

Nitrogen.

insulated, and covered to prevent personnel touching exposed

components.

• Ensure that the installation is inspected by a Specialist to confirm that it is

safe to use. Inspections must be carried out before the system is

commissioned and at regular intervals throughout its life.

• Pipework from the Dewar to the system must be adequately insulated and

connected to the system via a

” Swagelok connector.

Services Specifications

Issue 16: April 05 Page 16 of 22 Printed: 6-Jan-06, 8:44