Reduction of Vacuum Nipple Wear

Shamban & Microsystems TRIBOLOGY LABSDepartment of Mechanical EngineeringTechnion - Israel Institute of Technology

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Fretting motion as a reason of wear Test rig adjustments and sample preparation

Reduction of Vacuum Nipple WearMichael Varenberg, Yuri Kligerman, Haytam Kasem, Grigory Halperin, Alexey Tsipenyuk, Peter Breitman, Tamir Akhavan, Ariella Mansfield & Noam Rozen

Examination and testing of original chuck surfaces

Theoretical modeling of surface damage

To enable cyclic normal and tan-gential loading of contact projec-tions used in wafer chucking, wehave modified our test rig built forstudies of real contact area forworking in a flat-on-flat contactscheme (Fig. 3). The samplestested were cut from severalactual wafer chucks (Fig. 4)

250 µm

(a)

(b)

(c)

Fig. 1. Typical fretting damage. (a) An excessive amount offretting wear on a helicopter rear seat attach fitting. (b) Cracksappeared as a result of fretting fatigue in aircraft turbine bladedovetail joint. (c) Fatigue crack emanating from fretted zone.

Nominally motionless contacts sub-jected to cyclic load often originatingfrom vibration or temperature chan-ges may be damaged due to frettingmotion, which is defined as a rela-tive cyclic motion between two surfa-ces, having a non-uniform distribu-tion of local relative displacement attheir contact. Depending on loadingconditions, material properties andenvironment, fretting may cause fret-ting wear or fretting fatigue (Figs. 1and 2), which can arise in any as-sembly of engineering components.

Fig. 2. (a) Schematicof radial fretting de-veloping due to cyclicnormal loading alo-ne. (b) Contact areawith regions of stickand slip. (c), (d) Fra-gments of radial fret-ting wear scar at dif-ferent magnifications.

(a)

(b)

(c) (d)F

D

100 µm 10 µm

We acknowledge the support of the Israeli Ministry of Economy (METRO 450Consortium within the frame of MAGNET program). We thank Michael Gissin(Jordan Valley), Yoram Uziel (Applied Materials) and Ronen Peretz (Intel) forproviding chuck samples for tests.

X-Y table

Microscope stand

Microscope

Camera(a) (b) (c)

Normal loading lever

Tangential loading lever

Piezo drive

Weight holder

Self-aligning sample holderSample

Transparent sample holderTransparent sample

Fig. 3. (a) Schematic of experimental test rig. (b)Sample holders in assembly. (c) Sample holders andsamples in section view .

(a) (b) (c)

(e) (f)

(d)

Fig. 4. (a) Self-aligning sample holder. (b) Sample cut from (c)electrostatic chuck (Applied Materials). (d) Vacuum chuck (JordanValley) and (e) sample cut from it. (f) New vacuum nipple (JV).

Given the presence of relative motion, the forces exerted on the surface act through cer-tain distances so mechanical work is done on the surface. The amount of energy dissipa-ted in contact due to this work actually determines the form and severity of surface damage.

This allows usdefining a new we-ar criterion basedon specific energyand obtained byintegating frictionstress over slidingdistance (Fig. 7).Using this criterionwe have studiedthe effects of ma-terial and surfacegeometry on chuckwear (Fig. 8).

Fig. 8. Maximum work of friction forces (energy dissipated in contact) for two pairs of materials and differentgeometries. (a) Nipple by Jordan Valley. (b) Support projection by Applied Materials.

µ=0.33

µ=1.5

-60 kPa

0

0.002

0.004

0.006

0.008

0.01

0.0 0.2 0.4 0.6 0.8 1.0

Max

fri

ctio

n w

ork

, mJ/

m2

Pin radius, m

PVS

Al2O3

10

8

6

4

2

0

Si

-90 kPa

µ=0.33

µ=1.5

SiO2PVS

30

20

15

10

5

0

25

Max

fric

tion

wor

k, m

J/m

Max

fric

tion

wor

k, m

J/m

Max

fric

tion

wor

k, m

J/m

Max

fric

tion

wor

k, m

J/m

22 22

Fillet radius, mFillet radius, mFillet radius, mFillet radius, m0.250.200.150.100.050

(a) (b)

Fig. 7. Spatial evaluation of energy dissipated in contact due to the work of frictionforces in (a) nipple by Jordan Valley and (b) support projection by Applied Materials.

Friction stress

Sliding

Friction work

6

MPa

MPa

MPa

MPa

020

nmnm nmnm

060

mJ/

mm

J/m

mJ/

mm

J/m

22 22

03.082 3.083 3.090 3.161

Radial coordinate, mmRadial coordinate, mmRadial coordinate, mmRadial coordinate, mm

4020

51015

24 Friction stress

Sliding

Friction work

1.0

MPa

MPa

MPa

MPa

08

nmnm nmnm

04

mJ/

mm

J/m

mJ/

mm

J/m

22 22

00 0.1 0.2 0.3

Radial coordinate, mmRadial coordinate, mmRadial coordinate, mmRadial coordinate, mm

32

246

0.5

1

(a) (b)

20,000 Cycles

200 µm

0 Cycles 40,000 Cycles 60,000 Cycles

0 Cycles 60,000 Cycles 75,000 Cycles0 Cycles

(a) (b)

(c) (d)(e) (f)

(g) (h)

Fig. 6. Surface damage of the samples made from actual chucks and repeatedly loaded in normal direction only inlaboratory experiments. (a)-(d) Fragment of the contact area of the ceramic support projection (Applied Materials)loaded with 7 N and seen through the transparent sapphire counter-surface. Dark area visualizes the wear particlesaccumulated at the interface between the sample and sapphire window. (e), (f) Fragment of the contact area of theApplied Materials support projection before and after the test demonstrating wear particles accumulated on theprojection surface. (g), (h) The tip of the polymer support projection (Jordan Valley) before and after the testperformed under the load of 5 N demonstrating plastic deformation of the contact area.

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)

(j) (k) (m)

Fig. 5. Surface topography of (a)-(c) new and (d)-(i) worked nipples of Jordan Valley (fromchuck in Fig. 4d). (j) Worked chuck of KLA-Tencor and (k), (m) profiles of its vacuum groves.

Surface topog-raphy of newand worked (inreal machines)chucks wasexamined. Themeasurementsshow (Fig. 5)wear depths ofseveral micro-meters on ed-ges of workingsurfaces. Thetests perfor-med in the labshow the evo-lution of surfa-ce damageand accumula-tion of weardebris on wa-fer supports(Fig. 6) work-ing as a pollu-tion source.