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SEMI F20-0305 © SEMI 1995, 2005 10 Secondar y Electron Ima g e Mode Backscatter Electron Image Mode ( a ) Electrode 1: 1 w eld, 5 m isfires. ( b ) Electrode 2: 1 weld, arc failed in level 3 (c)Electrode 3: 1 w eld, arc f…

SEMI F20-0305 © SEMI 1995, 2005 9

A2-2.5.2 There appears to be a Cu/S interaction; the copper effect on welding is more pronounced at sulfur levels

under 0.010%.

A2-2.5.3 Commercially available tubing of 2.0 in. diameter and above is currently being offered with residual

copper levels above 0.2%.

A2-2.5.4 Cohen’s data shows that oxidation after welding will occur at 0.31% Cu, 0.010% S in argon; Collins’ data

shows an acceptable weld at 0.30% Cu, 0.011% S in argon.

A2-2.5.5 A cosmetically unacceptable weld, with bead meander and Cu redeposited in the HAZ, was found at

0.41% and 0.47% Cu.

A2-2.5.6 Heats above 0.30% Cu may be welded successfully in argon, but may exhibit bead meander and electrode

attack in Ar/H

(a) 2.5 in. tubing, Cu content 0.37%. Bead

meander condition became evident with addition

of H2 to shield gas.

(b) 2.5 in. tubing, Cu content 0.34%. Bead

meander condition became evident with addition

of H

to shield gas, worsened with each weld.

Figure A2-1

Weldability: Copper Content and Shield Gas Interactions

A2-2.5.7 Scanning electron micrographs of welding electrodes after welding 2.5 inch tubing with Cu content

0.34%; Shield gas Ar/H

SEMI F20-0305 © SEMI 1995, 2005 10

Secondar

Electron Ima

e Mode

Backscatter Electron Image Mode

(

)

Electrode 1: 1 weld, 5 misfires.

(

)

Electrode 2: 1 weld, arc failed in level 3

(c)Electrode 3: 1 weld, arc failed in level 3; Changed shield gas to Ar, welded acceptably; Changed

back to Ar/H, 2 welds, then misfired.

Figure A2-2

Weldability: Effect of Copper Content and Shield Gas on Weld Electrodes

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SEMI F21-1102 © SEMI 1995, 2002 1

SEMI F21-1102

CLASSIFICATION OF AIRBORNE MOLECULAR CONTAMINANT

LEVELS IN CLEAN ENVIRONMENTS

This classification 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 August 29, 2002. Initially available at www.semi.org September 2002; to

be published November 2002. Originally published in 1995.

1 Purpose

1.1 The purpose of this standard is to classify

microelectronics clean environments with respect to

their molecular (non-particulate) contaminant levels.

This standard classification provides a consistent means

of communicating acceptable contaminant levels of

groups of specific airborne molecular contaminants.

See Related Information 1 appended to this standard.

2 Scope

2.1 This standard classification is to be used in the

specification of semiconductor clean environments

(including process tool environments) and of

contamination control and measurement equipment

performance.

2.2 This standard does not purport to address safety

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

responsibility of the users of this standard to establish

appropriate safety health practices and determine the

applicability or regulatory limitations prior to use.

3 Referenced Standards

None.

4 Terminology

4.1 Definitions

4.1.1 acid — a corrosive material whose chemical

reaction characteristic is that of an electron acceptor.

4.1.2 base — a corrosive material whose chemical

reaction characteristic is that of an electron donor.

4.1.3 condensable — a substance (other than water),

typically having a boiling point above room

temperature at atmospheric pressure, capable of

condensation on a clean surface.

4.1.4 dopant — a chemical element which modifies the

electrical properties of a semiconductive material.

5 Basis of Classification

5.1 Classification is by the maximum allowable total

gas phase concentration of each category of material.

This classification system is depicted in Section 6. The

combination of a quantitative class for each of the four

categories yields a classification describing an

environment.

5.2 The maximum cumulative gas phase concentrations

of the four categories may be different.

5.3 Each category is designated by the letter “M,”

followed by the first letter of the category name A, B,

C, or D.

5.4 The integer following the category designator shall

indicate the maximum total gas phase concentration in

parts per trillion molar (pptm 1 ×10

-12

). For example, a

category MA-10 has a maximum allowable total

concentration of 10 parts per trillion molar for the

category of interest.

6 Classification

Material