Clean production for (ultra) high vacuum application

Clean production

for (ultra) high vacuum applications

Anton de Jong, Anton Duisterwinkel

2011-03-11

Themadag Schoon Produceren

1

Cleaning : Strategy

Step by step cleaning

1. Pre cleanRemoves film, visible dirt, gross contamination.

Can be manual, industrial dish washer is preferred

2. Particle removalRemoves particles and droplets to required level

Often involves wet cleaning, ultrasonic.

Rinsing is critical.

3. Molecular cleaningRemoves last molecules,

Drives off absorbed contaminants.

Preferably done shortly before use.

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2

Wet cleaningfilm removal by ultrasonic (US) cleaning

Result HV (UHV when combined with baking)

Procedure (after pretreatment)Place object well separated in rack; degas the water

Use optimized program (e.g.: ~ 50 kHz + sweep function;

low detergent concentration, 60-80 °C, 5-15 min)

Rinse plentiful with demiwater

first step with US but beware of cavitation

final step 60-80°C, but beware of oxidation

Blow dry with clean and filtered N2

Monitor program (T, t); water quality (pH, conductivity)

Damagedue to cavitation

Damage due to oxidation

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3

Cleaning molecular contamination

Pre clean is a must!

(for example wet cleaning, IPA rinse)

Baking in/of vacuum system

+ standard, proven; - high T, low P

Plasma

+ relatively cool; quick - low P, crevices

Solvent and vapour degreasing

+ good for high volume - environment, k€

UV-ozon (optical components)

+ low T, 1 bar, quick - line of sight, O3

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4

Bake out systems

Typical: 80-200 °C

Time : 5-50 hour

Clean air or nitrogen

Clean oven interior

Requirements bake out systems

• Stainless Steel interior

• Low or high vacuum pumping system

• Oil free: no polymers allowed (except for door seal)

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5

Qualification bake out systems

How to qualify chambers?

Outgassing measurement in case of HV system

Tenax testing with absorbent and GC/MS analysis

Witness sample with NVR testing, XPS analysis or FTIR spectroscopy

Requirements:

Outgassing: PCxHy < 10-12 mbar

Tenax: < LDL

Witness sample: <LDL

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6

What is a plasma?

Plasma is an ionized gas consisting of free electrons, ions, reactive

atoms, neutral molecules and photons

The plasma state can be reached by supplying sufficient energy

(heat or electric power) to a gas or mixture of gases

Cool plasma can be operated at low or at atmospheric pressures

Solid Liquid Gas Plasma

Add energy

H2O (s) H2O (l) H2O (g)

H,H2,H+,e-,H2

-

O,O2,O3,O-,O2

-H2O

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7

Plasma cleaning

Plasma + -Affordable Can attack surfaces (polymers!)

Can be cool (~40°C) Needs development/application

quick not for crevices, potholes, L>D

Options

Many different gas combinations

Different plasma production technology

Caging for milder plasma

Procedure

Develop proper process

Preclean

Monitoring is not straightforward (e.g. p, T, t, gas composition)

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8

Plasma generation

Typical pressure: either 0.1 and 10 mbar or 1 bar (atmospheric)

Plasma can be generated by several excitation sources:

RF (kHz and MHz)

MW (GHz)

DC

Several active species possible:

O2 (oxidative)

H2 (reducing)

Ar (sputtering)

SF6 (chemically)

He or air (atmospheric treatments)

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9

Plasma generation

Materials and components to be processed need to be checked for

compatibility with active species and generation process:

O2 can damage thin layers (silver coatings)

RF fields can induce eddy currents (CD in microwave oven) and damage

electronics

Plasma can be generated remotely or object is immersed directly in

plasma. Remote plasma is more gentle and slower

From open air / small reactor to container size commercially available

(but no cleaning recipe or process included)

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10

Product cleanliness qualification

Dedicated set-up built for automated

baking and testing of assemblies

(including report generation)

Small system for testing components,

materials and electronic devices

TNO TNO

Baking Small RGA set up

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11

Most commonly used is a Quadrupole Mass Spectrometer

(QMS), also known as a Residual Gas Analyser (RGA)

How does a mass spectrometer work:

Ionise molecules

Filter ions according to

the mass/charge ratio

Detect ions

Rest Gas Analysis

RGA head and controller

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12

Slide 12 |

RGA interpretation

Peaks can be several components and

one component can have several sources

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13

Typical result of RGA measurement

Ion current per mass (one or more compo-nents)

H+ H2+ H2O

N2CO2

Logaritmic scale: ten times more H2

than CO2

Measured with total pressure gauge

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14

Interpretation of RGA measurements (1)

Mass spectrum after 8h pumping(pressure corrected)

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1 21 41 61 81 101 121 141 161 181

Mass [amu]

Pre

ss

ure

[m

ba

r]

Sample + background Background

CF3+ C2F4+

C2F3O+

C2F5+C2F5O+

C3F6+

C3F5+

C3F5O+

C3F7+

C3F7O+

leak

(N2:O2~4:1 & Ar)

leak

(N2:O2~4:1 & Ar)

slight permeation

through O-ring

RGA-plot of seal with additional o-ring

Compare to background (blue)

Peaks at distinct masses point to distinct contaminants

High peaks of N2,O2 and Ar:air leaking in, butnot at “air” ratio’s

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15

Results

KF 10 blind flange made from SS316 with

Laser sintering (Rapid Manufacturing)

Mass spectrum after 10h pumping(pressure corrected)

1.E-15

1.E-14

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

0 20 40 60 80 100 120 140 160 180 200

Mass [amu]

Pre

ss

ure

[m

ba

r]

Sample + background Background

Outgassing versus time

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

0 2 24

Time [hours]

Q [

mb

ar.

l/s

]Integrated

CxHy

Integrated (background)

CxHy (background)

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16

RGA: typical uses

Qualification of vacuum systems

Compare results to requirements

Leak detection

Look for typical air peaks (N2, O2 and Ar)

Scan He for leak searching

System cleanliness

Look for CH2-bumps and specific components

Outgassing tests

Dedicated chamber with known background

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17

Theoretical

efftottot SPQ *=

Total outgassing:

Water outgassing:

Hydrocarbon outgassing:

Other combinations possible

efftot

i

SPP

PQ *

200

1

18

18

∑=

efftot

i

i

HC SPP

PQ

yx*

200

1

100

44

∑

∑=

No correction for ionisation efficiencies

Results are in nitrogen equivalent pressures

Volatile hydrocarbons:

Non volatile hydrocarbons:

efftot

i

i

HC SPP

PQ

yx*

200

1

200

44

∑

∑= efftot

i

i

HC SPP

PQ

yx*

200

1

200

101

∑

∑=

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18

A typical system

• Magnetic turbo for hydrocarbon free

pumping

• Granville Phillips Stabil Ion

pressure gauge

• Pump speed reduced to 25 l/s

• Pfeiffer QMG422 RGA

• Load lock

• Heated sample holder

• Electrical connections for testing

devices under power

Pult = 5*10-9 Pa

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19

Measurement procedure

Vent loadlock with dry nitrogen

Open loadlock

Place sample on transporter

After 5 minutes close loadlock and

start pump

When pressure is below 1*10-4 Pa

transfer sample to Main Chamber

Start measurement for 10 hours

minimum

Background measurement performed

with empty sampleholder

Laser sintered KF10 blind flange made with Rapid Manufacturing

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20

RGA: operating tips

Do NOT use RGA when total pressure > 1*10-4 mbar, this will cause

filament burn-out

If equiped with Secondary Electron Multiplier do not operate this

above 1*10-6 mbar

A RGA needs to warm up before accurate measurements can be

taken (> half hour)

Selection, use and interpretation of RGA is specialist job!

Beware: RGA is a source of

Heat (due to filament)

electric fields (due to magnetic field for separation)

Light (due to heated filament)

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21

RGA: what you need to remember

Partial pressure = how much of each component makes up of total

pressure

RGA is very useful to determine gas composition (partial pressures)

Used for qualification of systems and parts and leak testing

Only determines partial pressure

Spectrum analysis is a specialist job

Years of experience and training needed

Do NOT switch on RGA when pressure > 10-4 mbar

Clean production for (ultra) high vacuum application

Documents

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generation process

remote plasma