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SEMI F41-0699 © SEMI 1999 3 purity chemical flus hed t o drain during the qu ali ficat ion process, this approach m ay also prove to be m ore cost effective depending on the cost of the chemical used for pickling, compar…

SEMI F41-0699 © SEMI 1999 2

4.2.1 SIA National Technology Roadmap For Process

Chemicals

5 Terminology

5.1 Acronyms and Abbreviations

5.1.1 BCDS — Bulk Chemical Distribution System

5.2 Definitions

5.2.1 pickling — To condition the BCDS by exposing

to an aggressive chemical that extracts impurities from

the internal surfaces of the system.

5.2.2 sample — Sample taken from a system into a

sampling container and measured off-line.

6 Pre-Chemical Qualificatio n

6.1 Advantage of Pre-Chemical Qualification — The

pre-chemical qualification is designed to ensure that the

piping systems and storage tanks are able to accept

chemicals. This step is often initiated after the UPW

system is functional and an acceptable resistivity is

achieved but before chemicals are authorized to be

brought on-site. Although UPW does not extract high

levels of metallic and ionic impurities from the BCDS

materials of construction, this step can ensure that the

BCDS and distribution piping is free of any gross

contamination that may have been introduced into the

system during installation. In addition, the UPW flush

can be effective for the elimination of some types of

particles.

6.2 Particle Qualification  The BCDS is flushed

with UPW and the levels of particles are measured

using an on-line optical particle counter. The steps

followed include:

6.2.1 Install an acceptable UPW water filter element(s)

per the filter and BCDS manufacturer's specifications.

6.2.2 Fill the BCDS with UPW and recirculate

internally to ensure that all piping is filled with UPW.

6.2.3 Begin sampling to a liquid particle counter

downstream of the filters either at the outlet of the

BCDS, the POU, or both. Follow an approved particle

counting sampling procedure.

6.2.4 Continue recirculating and flushing until the

particle concentrations in the desired channel or

channels are observed at levels below the agreed-upon

specification. An example of typical specification is the

average of five consecutive ten minute readings of <X

particles/ml @ ≥ Y micron.

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95110, USA

6.3 Metallic Qualification  After reaching the

particle specification for the UPW, a sample of UPW

may be taken for trace metal analysis. This sample can

be taken at the outlet of the BCDS, at an end point

sample station and/or at the POU. An appropriate

sample bottle precleaned for this test should be used to

collect a sample. The sample bottle should be

preconditioned before use and contamination-free

techniques used for the actual sampling.

6.3.1 The steps to follow are:

6.3.1.1 Fill the sample bottle with the required volume

for the analytical method to be used. The volume varies

depending on analytical procedures and lab

instrumentation.

6.3.1.2 Send samples to a designated laboratory

capable of performing trace metal analysis. Use only a

laboratory that has experience with these types of

samples and that can test reliably in the sub-ppb range.

The number of elements and concentrations that are to

be analyzed will vary depending on customers’

requirements.

6.3.1.3 Evaluate data and compare to the agreed-upon

specification. A typical specification is <X ppb total

and <X ppb per element.

6.3.1.4 If the trace metal specification is not met, drain

or flush the entire BCDS and distribution piping and

repeat the process.

6.3.1.5 If a maximum level of impurities is desired, a

sample of the UPW used to charge the system should be

tested to establish a baseline and to ensure that the

incoming UPW is not the source of high impurities.

6.3.1.6 Once the BCDS has been qualified for particles

and trace metals in UPW, the qualification of the BCDS

in Chemical may be initiated.

7 Chemical Conditioning of The System

7.1 Advantages of Conditioning the System 

Another precleaning step that may be used

independently or in conjunction with a UPW flush is to

condition the BCDS by actively flushing it with an

aggressive chemical that extracts impurities from the

internal surfaces of the system. This step is sometimes

referred to as "pickling" the system. This extra step can

help minimize the amount of time consumed in the

qualification process by utilizing a chemical with more

aggressive extraction properties than the actual

chemical to be used in the line, thereby increasing the

rate at which impurities are removed. This can shorten

the amount of time needed until the actual chemical can

be put into the line and shown to meet the qualification

specifications. Since a goal of a well-designed

qualification protocol is to minimize the amount of high

SEMI F41-0699 © SEMI 19993

purity chemical flushed to drain during the qualification

process, this approach may also prove to be more cost

effective depending on the cost of the chemical used for

pickling, compared to the cost of the process chemical

designated for use in the line.

7.2 Conditioning With Same Chemical  A variation

on the above approach is to "pickle" the system with the

process chemical that is intended to be used in the

BCDS line a 24-72 hour soak period and flushing the

chemical to drain. While the process chemical may not

be as aggressive in cleaning up the line, this approach

has the advantage that the extracted metals have the

same fingerprint as those that might otherwise be

observed during the final qualification testing, and the

final qualification may be done immediately following

this step, without further preparation.

7.3 Testing the Preconditioning Chemical  Rather

than relying on an arbitrary or predetermined lengths of

time for preconditioning the BCDS, test samples are

often taken and analyzed to ensure that the required

level of impurities has actually been obtained. This

testing is often commissioned by the equipment

manufacturer and not reported to the customer as part of

the BCDS qualification. Indicator elements are often

analyzed that are either of particular concern in the

process chemical, or elements such as Ca, Cr, Cu, Fe,

Mg, Na, Ni, and Zn, that are known as common

impurities in chemicals and that are also highly

detrimental in semiconductor processing.

7.4 Conditioning Procedure  The three most

common chemicals (HCL, HF, and HNO3) used for

precleaning the BCDS are aggressive in extracting

metallic impurities and particles. The steps followed

include:

7.4.1 Install an acceptable chemical filter element(s)

per the filter and BCDS manufacturer's specifications.

7.4.2 Fill the BCDS and distribution piping with the

chemical of choice and recirculate internally to ensure

that all piping is filled. This may include all

distribution piping. Let the chemical soak the materials

of construction in a static manner for a period of 24 to

72 hours, or continue recirculating the chemical as a

closed loop for the same amount of time.

7.4.3 Flush the chemical from the system.

7.4.4 Depending on the chemical used, a UPW rinse

step or an inert gas purge step for drying may be

required prior to filling the system with the actual

chemical for the qualification testing.

Note: The precleaning chemicals used may add

undesirable contaminants (i.e. F

from Hydrofluoric

acid, Cl

from hydrochloric acid, etc.). Therefore, if

any of these chemicals are used, additional testing may

be required to determine that these materials have not

added contaminants in excess of any specification.

These contaminants may be tested in the UPW rinse

step or in the final chemical qualification step.

7.5 Solvent Systems  The type of chemical used for

flushing solvent BCDS systems is different than that

used for oxidizers and corrosive chemicals since solvent

systems can be made from stainless steel and metal

materials for reasons of safety and chemical

compatibility. Generally, IPA, or the chemical to be

used in the system, is used for the aqueous pre-clean

step in flushing a system where solvents are to be used.

8 Final Chemical Qualification

8.1 Initial Considerations  Notwithstanding any of

the steps taken to prepare the BCDS for qualification

testing, certain issues should be considered prior to

starting any sampling required in the qualification

process:

8.1.1 Determination about the adequacy of the

sampling points.  The sampling points are generally

coincident with the location of pre-existing sample

ports on the Valve Manifold Box, day tank and other

distribution points. The adequacy of the sampling

points depends on their accessibility, environmental

controls, ability to flush prior to sampling, and safety

considerations.

8.1.2 Adequacy of data.  Due to sampling error,

possibility of environmental contamination, handling

problems, and impurities in sampling containers,

samples should be taken in duplicate or triplicate, with

two samples sent to the lab for testing and one sample

retained in case of a dispute.

8.1.3 Use of proper precleaned samp ling containers.

 Sampling containers must be chemically compatible

and precleaned in a manner consistent with the desired

specification level for impurities. Sample bottle

preparation differs depending on the type of testing to

be performed.

8.1.4 Use of a contamination-free sampling device for

samples pulled from an open vessel or a drum.

8.1.5 Proper training for personnel a ssigned to

sampling.  The proper training is required to ensure

that personnel charged with sampling follow

appropriate safety and contamination-free protocols.

SEMI F41-0699 © SEMI 1999 4

8.2 Particle Qualification  For most accurate results,

particle levels should be measured on-line with a

optical particle counter capable of measuring the size of

particle that is included in the guaranteed specification.

Batch samples may be taken and measured for particles

in a lab, but special care is needed to prequalify

containers used for this sampling, and data integrity

may be compromised for the smallest sized particles

due to various contamination sources. An example of a

protocol generally followed to measure particle on-line

includes:

8.2.1 Remove all UPW in the BCDS and distribution

piping.

8.2.2 Remove UPW filters or replace incompatible

chemical filters if present.

8.2.3 Install specified filter element per the BCDS and

filter manufacture's specifications.

8.2.4 Commission the BCDS and distribution piping

with the process chemical.

8.2.5 Recirculate chemical through the BCDS and

through all POU to drain.

8.2.6 Drain all chemicals from the BCDS and

distribution piping.

8.2.7 Refill entire system with chemical and begin

circulation through filters and out to POU to drain.

8.2.8 Begin sampling to a liquid par ticle counter

downstream of the filters either at the outlet of the

BCDS, the POU, or both. Follow a prescribed particle

counting sampling procedure.

8.2.9 The number of particle samples and sample

duration time should be calculated based on the total

volume of chemical desired to be examined by the

particle counter. A "sufficient" volume of chemical

should be examined by the particle counter during the

qualification period. As an example, the particle

concentration could be measured over at least a five-

hour period with thirty consecutive ten-minute samples

taken. In this example, the average of the last

consecutive 30 samples would be calculated and

compared to the specification.

8.2.10 The particle concentration is considered

acceptable if the average is less than the specification.

8.3 Metallic Qualification  Metallic impurities are

generally specified both in terms of level of impurity by

element and total amount of impurities. The customer's

specification generally lists each element to be included

in the analysis or may refer to the list of elements

published by SEMI for each chemical at different purity

grades. The maximum impurity levels may be

described as an absolute value (e.g. 1ppb maximum

impurity), or in terms of the quantity of impurities that

may be added by the BCDS including the distribution

piping. This amount of "total adders" is determined by

measuring the impurity levels of the incoming chemical

from the storage or supply vessel compared to the

purity level of the chemical at the end point sample

station or POU. The number of samples and location of

samples vary depending on the type of specification.

When qualifying to a “metallic impurities added”

specification, a sample must be taken from the

incoming chemical supply drums for an incoming

baseline. The testing protocols includes:

8.3.1 Precondition all sampling bottles before use and

follow appropriate sampling protocol.

8.3.2 Send samples to a lab for trace metal analysis

specifying the level of testing required and the number

of elements to be tested. The level of testing required

depends on the agreed upon specification. As a rule of

thumb, the detection limits of the analysis should be at

least 10X's lower than the impurity level to be achieved

for each element. In addition, the lab should follow

high standards of quality control for trace metal

analysis including analysis in duplicate, duplicate

blanks, use of internal standards, instrument calibration

using primary standards, and QC checks.

8.3.3 Review the data that is reported and compare it

to the customer requirement.

8.3.4 If the system does not meet the specification

then repeat the procedure until the system is qualified.

8.3.5 Where maximum levels of impurities are

specified, a sample of the incoming chemical should

either be measured as part of the qualification process,

or retained, to ensure that the incoming chemical is not

a significant source of contamination.

8.3.6 For purposes of metallic qualification, soak

periods similar to those referenced in Section 7.2 are

recommended.

9 Other Considerations

9.1 Accelerated Qualification Techniques 

Although process chemicals such as hydrofluoric and

hydrochloric acid may reach acceptable levels of purity

after a few weeks in the BCDS, other chemicals such as

sulfuric acid and ammonium hydroxide extract

impurities much more slowly and significant levels of

impurities are observed even after several months. The

BCDS conditioning process described above is one

approach to preleaching impurities from the BCDS.

Other variations include combinations of static and

dynamic rinses and emphasis on the use of dilute HF as

the aqueous preclean chemical that is particularly

effective for iron removal, however, it contributes high