Calibration of areal surface texture measuring instruments

Richard Leach

DMAC, 2006, University of Huddersfield

Introduction

• Current trend in industry is towards areal (or 3D) surface texture measurement

• Liam has already discussed the benefits• There are many areal instruments on the market

including stylus and optical systems• But, there is at present no route to traceability (well not

quite yet!)• Profile artefacts are used to give limited traceability

Aspects of instrument performance to be addressed by areal artefacts:

• XY resolution

• XY positional error

• Z positional error

• Dynamic performance

• Tip condition monitoring

• Roughness parameters (S-parameters)

X Y Resolution

0.6

0.8

1.0

1.2

1.4

1.6

2

6

10

1

2

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7

8

Grating patterns e-beam written on silicon. Chips are 12 mm square, carrying an array of 9 test patterns

Chip Res A carries 9 gratings of pitches 0.6 to 10 µm.

Chip Res B carries 8 gratings of pitches 1 to 8 µm and an array of star patterns in the central patch.

Res A

Res B

0 200000 400000 600000 800000 nm

nm

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XY positional error

Chrome on glass grid patterns

• 20 µm wide lines at 200 µm pitch

•10 µm wide lines at 100 µm pitch

•5 µm wide lines at 20 µm pitch

Z positional error

•Step heights covering the range 10 nm to 50 µm

•Widths compatible with field of view of optical systems

•Waffle patterns to check z positional error over image area

Diamond turned master for step heights 1 µm to 50 µm

1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6n m

-1 0 0 0-8 0 0-6 0 0-4 0 0-2 0 0

02 0 04 0 06 0 08 0 0

0 2 0 0 0 0 0 4 0 0 0 0 0 6 0 0 0 0 0 8 0 0 0 0 0 1 0 0 0 0 0 0 1 2 0 0 0 0 0 1 4 0 0 0 0 0 n m

M e a n va l u e s o n 1 6 ste p s.

M a x i m u m d e p th 9 9 3 n m

M e a n d e p th 9 9 0 n m

W i d th 2 3 6 1 7 n m

Silicon waffle pattern 1 µm step height

Z positional error

Diamond turned steps, replicated in nickel

50 µm step

100 µm wide

Imaged by white light interferometry, X50 lens

53239 nm

365892 nm

359707 nm

Alpha = 25° Beta = 39°

1 2nm

-30000-20000-10000

0100002000030000400005000060000

0 50000 100000 150000 200000 250000 300000 350000 nm

1 2

Maximum depth 49607 nm 49714 nm

Mean depth 49573 nm 49697 nm

Width 66808 nm 81224 nm

Z positional error

30 µm pitch waffle pattern 100 µm pitch

waffle pattern

200 µm pitch waffle pattern

Layout of the silicon step standards

Broad and narrow lines may be calibrated using ISO 5436 method for stylus profilometers

Z positional error0 500000 1000000 1500000 nm

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1nm

-1400-1200-1000

-800-600-400-200

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0 200000 400000 600000 800000 1000000 1200000 1400000 1600000 nm

1

Maximum height 992 nm

Mean height 992 nm

Width 161719 nm

500 µm wide1 µm step

1nm

-1400-1200-1000

-800-600-400-200

0200400

0 50000 100000 150000 200000 250000 300000 350000 nm

1

Maximum height 993 nm

Mean height 993 nm

Width 31641 nm

100 µm wide

Z positional error

1 µm waffle pattern

1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6n m

-1 0 0 0-8 0 0-6 0 0-4 0 0-2 0 0

02 0 04 0 06 0 08 0 0

0 2 0 0 0 0 0 4 0 0 0 0 0 6 0 0 0 0 0 8 0 0 0 0 0 1 0 0 0 0 0 0 1 2 0 0 0 0 0 1 4 0 0 0 0 0 n m

M e a n va l u e s o n 1 6 ste p s.

M a x i m u m d e p th 9 9 3 n m

M e a n d e p th 9 9 0 n m

W i d th 2 3 6 1 7 n m

Z positional error

10 nm waffle pattern

nm

-15

-10

-5

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0 100000 200000 300000 400000 500000 600000 700000 800000 nm

Length = 877610 nm Pt = 18 nm Scale = 30 nm

nm

-60-50-40-30-20-10

010203040

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 mm

Length = 0.55 mm Pt = 105.68 nm Scale = 110 nm

nm

-60

-40

-20

0

20

40

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 mm

Length = 2.6187 mm Pt = 110.23 nm Scale = 120 nm

Narrow Step 100-2

Broad step100-2

nm

-10-8-6-4-202468

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 mm

Length = 0.5484 mm Pt = 11.353 nm Scale = 20 nm

nm

-10-8-6-4-202468

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 mm

Length = 2.6203 mm Pt = 15.175 nm Scale = 20 nm

Narrow Step 10-3

Broad step10-3

Glass steps

Typical stylus traces

Dynamic performance

Series of sine wave profiles generated by diamond turning:

2.5, 8 and 25 µm pitch

max slope angles 5˚ and 20˚

Fourier transforms25 µm sine waves

Deep (20°max slope)

shallow (20°max slope)

harmonic distortion < 4%

Tip condition monitoring

θ= 60˚

Series of cusped profiles generated by diamond turning and replication

Random roughness

Require

•isotropic surface

•single material

•translationally and scale invariant

•low surface slopes

Manufacturing methods investigated:

•Fine sand blasting

•EDM and polishing

•Chemical vapour etch on glass

Random roughness

0 0.5 1 1.5 mm

mm

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

µm

01234567891011121314

µm

-10-8-6-4-202468

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 mm

Length = 1.8 mm Pt = 11.8 µm Scale = 20 µm

EDM surface

electro-polished

A traceable instrument

• So, we now have the transfer artefacts – what about a traceable instrument?

• Should we use a stylus or optical system?• Are there commercial instruments that fit the bill?• What about software?

A traceable areal surface texture measuring instrument – xy metrology

• Working volume 10 mm x 10 mm x 0.1 mm to an uncertainty of 10 nm x 10 nm x 1 nm

• Uses co-planar xy air bearing, 4 dof of interferometry, autocollimators and a 3 mirror block

• Mathematical model applied to process the data

A traceable areal surface texture measuring instrument – z metrology

• Probing system in z is a stylus design that probes through one of the mirrors

• Motion controlled by an air bearing (FFD) and an electro-magnetic spring

• Uses differential interferometry to “remove” the effect of the metrology frame

xy translation stage

Mirror for x or y interferometry Sample

z mirror

Stylus and mirror assembly

Air bearing Lens

Reference beams Measurement beams

Toroidal magnet

Coil

A traceable areal surface texture measuring instrument

“First surface” August 2006 plus results of an industrial comparison (UK)

Conclusions

• We now have the ability to produce areal transfer artefacts

• ISO 213 is now producing technical specifications that will become standards in around three years (ha ha!)

• We now have an instrument that can measure traceblyareal surface texture

• But, we still need reference software for areal parameters, filtering, etc.

• We also need to consider uncertainties…