semi合集-English.pdf - 第125页

SEMI E17-0600 © SEMI 1991 , 2000 1 SEMI E17-0600 GUIDELINE FOR MA SS FLOW CONTROLLER TR ANSIENT CHARACTERISTICS TESTS This g u ideline was tec hnically approved by the Global Fa cilities Committee and is the direct respo…

SEMI E16-90 © SEMI 1990, 2004 3

Interval Rate Example

t1 Initial System Response Less than 10 seconds

t2 Leak Prior to Onset of

Permeation

w1 10 seconds to 1 minute

t3 Increasing Permeation 1 minute to 30 minutes

t4 Total Saturation w2 Beyond 30 minutes

Figure 4

Leak Detector Output Value vs. Time

4.3.1 The actual shape of these curves and time

intervals is dependent on the design of the MFC under

test, the elastomer used, if any, and the characteristics

of the leak detection system. These time intervals must

be determined using sound engineering judgment

following qualification testing of the specific MFC

model and test set-up. Once determined, it is

recommended that receiving inspection consist of

measuring for leak rate value w1 at the end of interval

t2.

4.3.2 Following qualification testing, report typical

values for t1 through t4 and w1 and w2. w1 is primarily

the mechanical portion of the leak, and w2 is

mechanical plus permeation. In the case where w2 is

significantly greater than w1, w2 is primarily

permeation. In the case of a gross mechanical leak, w1

could greatly exceed, and thereby mask, w2.

NOTE 3: This test must be performed with elastomers that

are devoid of helium. Such elastomers have either not been

previously exposed to helium or have been degassed

following exposure. Once this test has been performed, the

elastomers must be purged of helium by the passage of time

and/or baking.

4.3.3 In good leak testing practice, the background

level should be verified before the application of helium

to ensure that the elastomers are in a helium degassed

state and that the leak detecting system is in proper

operation.

NOTICE: SEMI makes no warranties or

representations as to the suitability of the standards set

forth herein for any particular application. The

determination of the suitability of the standard is solely

the responsibility of the user. Users are cautioned to

refer to manufacturer's instructions, product labels,

product data sheets, and other relevant literature,

respecting any materials or equipment mentioned

herein. These standards are subject to change without

notice.

By publication of this standard, Semiconductor

Equipment and Materials International (SEMI) takes no

position respecting the validity of any patent rights or

copyrights asserted in connection with any items

mentioned in this standard. Users of this standard are

expressly advised that determination of any such patent

rights or copyrights, and the risk of infringement of

such rights are entirely their own responsibility.

International), 3081 Zanker Road, San Jose, CA 95134. Reproduction of

the contents in whole or in part is forbidden without express written

consent of SEMI.

SEMI E17-0600 © SEMI 1991, 20001

SEMI E17-0600

GUIDELINE FOR MASS FLOW CONTROLLER TRANSIENT

CHARACTERISTICS TESTS

This guideline was technically approved by the Global Facilities Committee and is the direct responsibility of

the North American Facilities Committee. Current edition approved by the North American Regional

Standards Committee on April 10, 2000. Initially available at www.semi.org April 2000; to be published

June 2000. Originally published in 1991.

1 Scope

1.1 This guideline is intended to establish a common

basis for communication between users and suppliers of

semiconductor equipment. It provides terminology and

methodology aimed at eliminating confusion regarding

what previously has been referred to as MFC “response

time.” The conditions and procedures are given for

determining and expressing the transient characteristics

of a mass flow controller (MFC) to a step change in set

point. This guideline applies to mass flow controllers

for gases used in semiconductor fabrication equipment.

1.2 This guideline does not purport to address safety

issues, if any, associated with its use. It is the

responsibility of the users of this guideline to establish

appropriate safety and health practices and determine

the applicability of regulatory limitations prior to use.

2 Definitions (Figures 1 and 2)

2.1 Actual Flow — For the purpose of this standard,

the output value of the master reference standard.

2.2 Dead Time — The interval of time between the set

point step change and the start of the resulting

observable response.

2.3 Final Steady State Value — The average value of

the actual flow, after the effects of the input transient

have expired to a value equal to or below the intrinsic

drift and noise.

2.4 Settling Time — The time between the set point

step change and when the actual flow remains within

the specified band.

2.5 Step Response Time — The time between the

setpoint step change and when the actual flow first

enters the specified band.

2.6 Transient Overshoot — The maximum change in

actual flow minus the steady state change in actual

flow, expressed as a percentage of the set point step

change.

2.7 Transient Undershoot — The maximum amount

that the actual flow passes the final steady state value,

in the opposite direction of overshoot, expressed as a

percentage of the set point step change.

2.8 Set Point — The electrical input signal to the MFC

which sets the desired value of the controlled flow.

2.9 Specified Band — The region between ± 2% of the

final steady state value or ± 0.5% of full scale,

whichever is greater.

3 Test Setup

3.1 The purpose of the flow system is to furnish the

mass flow controller under test with a constant pressure

supply of suitable gas. It must also provide a means of

determining the gas flow rate through the mass flow

controller that responds to changes in gas flow

significantly faster than the device under test. The

recommended flow system for testing the speed of

response of MFCs is shown in Figure 3a.

3.2 The flow system shall have straight tubing or pipe

connecting the MFC to the master reference standard.

The inside diameter of the interconnecting tubing or

pipe shall be of sufficient size to preclude any pressure

drop that would affect the performance of the MFC.

3.3 The pneumatic time constant, Tau, should be

minimized. (See Section 3.7.)

Tau = (V*DPm) / (Qm*Pa)

Where:

V = Internal volume of the flow system between the

MFC under test and the master reference standard,

including tubing, fittings and the side of the master

reference standard that is connected to the MFC

under test.

Qm = Maximum volumetric flow expected during the test.

DPm = Pressure drop of the master reference standard at

flow Qm.

Pa = The absolute pressure present at the outlet of the

master reference standard at final steady state value.

3.4 The source of the test gas shall be capable of

delivering an essentially constant upstream pressure to

the mass flow controller under test during the transient

characterization. A maximum variation of ± 2% from

the median absolute pressure is considered adequate for

most mass flow controllers.

3.5 Nitrogen is the recommended gas for the standard

test shown in Figure 3a. The inlet pressure is 25 psig

(1.75 kg/cm

G). Outlet pressure is the prevailing

atmospheric pressure. The temperature of the gas

entering the flow controller and the temperature

surrounding the flow controller shall be the same.

Neither shall vary during the test so as to have a

significant effect.

3.5.1 The preceding conditions are recommendations.

Deviations may be made to more accurately reproduce

the conditions that the MFC will experience in use,

such as the variation shown in Figure 3b. Any deviation

from the above gas and pressure conditions and/or test

setup must be noted with the test results.

3.6 The master reference standard is used to provide a

representation of the instantaneous actual flow. It is

customary to refer to the output of the master reference

standard as the actual flow. It shall have an accuracy of

± 5% of reading (including linearity), or better, over the

flow range for which results will be reported. The

pressure drop across the master reference standard at

the test flow shall be small enough to not effect the

response of the MFC under test.

3.6.1 Typical master reference standards are Hot-Wire

flow meters (or similar immersible thermal flow

sensors), laminar flow elements with a differential

pressure transducer, and Rate of Rise (RoR) systems.

3.7 The measuring system response time is the sum of

the pneumatic time constant, master reference response

time and the recording system response time. The

measuring system response time shall be less than 1/5

of any reported transient characteristic. If the measuring

system response time is greater than 1/5 of a specific

transient characteristic, that characteristic may be

reported if the measuring system response time is also

reported.

3.8 The test setup shall provide a step change in the

setpoint to the mass flow controller, along with a time-

zero cue to the data acquisition system. The step change

transient time shall be less than 1% of the step response

time of the MFC under test.

3.9 The test setup is recommended for MFC full scale

flow rates above 10 sccm. In those cases where the flow

rate is below 10 sccm and the pneumatic time constant

is not less than 1/5 of the step response time of the

MFC the pneumatic time constant shall be reported.

3.10 The MFC shall be electrically energized for the

supplier recommended “warm up” time prior to the start

of the test.

Figure 1

Definitions of MFC Transient Characteristics Terminology in the Case

Where the Final Set Point Is Higher than the Initial Set Point