Small Angle X-ray Scattering Metrology for Sidewall Angle and

Small Angle XSmall Angle X--ray Scattering Metrology for ray Scattering Metrology for Sidewall Angle and Cross Section of Nanometer Sidewall Angle and Cross Section of Nanometer

Scale Line GratingsScale Line Gratings

Wen-Li Wu

Ronald L. Jones, Tengjiao Hu, Christopher L. Soles, Eric K. Lin,

Funding•NIST Office of Microelectronics Programs

[email protected]

ULSI, Richardson, TXMarch 18, 2005

• Introduction

•Measurement of pitch and line width

•Measurement of side wall angle & height

•Line roughness including both side walls & top surface (on-going)

•Conclusions


Critical Dimension Small Angle XCritical Dimension Small Angle X--ray ray Scattering (CDScattering (CD--SAXS)SAXS)

ω

2θ

Transmission SAXS•Silicon transparent for E > 13 keV•Developed using synchrotron technology•Non-destructive / No sample prep•Lab-scale device feasibility (in progress)

•Use scatterometry targets•Beam spot size (40x40) µm•Collection time: (1 to 5) seconds/sample•Model fits simpler than scatterometry

•Measure “2-D” and Buried patterns of metals & dielectrics•Via, post, pads, etc

• High Precision for small line width (10-300 nm)•Sub-nm precision in pitch and linewidth•Sidewall angle and Pattern Cross Section

•Technique “easier” with smaller structuresULSI, Richardson, TX

March 18, 2005

Top down SEM of dense array of via pads

2-D and Buried Structures

•Structures can be buried (metrology of 3-D circuits possible)

•Transmission measurement samples all depths equally

•2-D detector allows single measurement to characterize entire top-down shape.

•Additional measurements provide pattern cross section (I.e. sidewall angle)

•Full 3-D characterization possible of dense, high aspect ratio patterns

Resulting CD-SAXS detector image shows 2 axes of diffraction. Entire top-down shape can be characterized in one measurement


A Wide Range of SamplesA Wide Range of SamplesDense (1:1 spacing) 550 nm lines

Materials measured nonMaterials measured non--destructivelydestructively••Photoresists (248 nm, 193 nm, EUV)Photoresists (248 nm, 193 nm, EUV)••Engineering Polymers (PMMA, PS)Engineering Polymers (PMMA, PS)••Oxides (SiO2)Oxides (SiO2)••Nanoporous MatricesNanoporous Matrices••Barrier layers (Barrier layers (SiNSiN, , SiCNSiCN))••Metal Interconnects (Cu)Metal Interconnects (Cu)

Pattern GeometriesPattern Geometries••Line/Space patterns (gratings)Line/Space patterns (gratings)••Arrays of columnsArrays of columns••Arrays of holes (Arrays of holes (viasvias))


Hexagonal Close Packed 60 nm vias

Line/Space Patterns in Oxide

Sparse (1:10 spacing) 15nm lines

6

7

8

91000

2

3

Inte

nsity

0.350.300.250.200.150.100.050.00

qx (nm-1)

Model Name: Rectangle Period (nm): 173 Line Width (nm): 15 Line Height (nm): 370 Dev. in Period (nm): 4 Pattern SLD (cm^-2): 1e+10 Scale Factor: 6 Background: 600

FILE: ISMT_S103_R_046.dat

Critical Dimension Small Angle XCritical Dimension Small Angle X--ray ray Scattering (CDScattering (CD--SAXS)SAXS)

• Probing wavelength < 1 Å → measurement becomes easier as feature size gets smaller

• Weak interaction between materials ( Cu, Ta, Si, C, O, H, etc.) → penetration power & Fourier transform (real objects)

• Absorption edge exists for heavy elements including Ta


challenges

• Quantify imperfections of nano-pattern from X-ray data

• Availability of intense x-ray source other than synchrotron


• Introduction


•Measurement of side wall angle and height


•Conclusions


SAXS characterization technique

• Pitch Measurement

D = 237.1 ± 0.5 nm

-10 -5 0 5 100.000

0.005

0.010

0.015

0.020

0.025

0.030

q (A

-1)

Peak orderD


6

7

8

9

1000

2

3

Inte

nsity

0.350.300.250.200.150.100.050.00

qx

(nm-1

)


• Average line width

0.000 0.006 0.012 0.018 0.024 0.030

102

103

104

105

experimental rectangle model, resolution function,

Debye-Waller effect

Inte

nsity

q (A-1)

W

Width = 128 nm


• Introduction


•Measurement of side wall angle


•Conclusions


Trapezoid as a starting point


Sidewall Angle MetrologySidewall Angle Metrology

Theoretical Model of Trapezoidal Cross SectionTheoretical Model of Trapezoidal Cross Section

βx

z

y

Qz

Qx

22--D Fast Fourier TransformD Fast Fourier Transform

+/- β


qx

qz

I



0 0.005 0.01 0.015 0.02-0.01

-0.005

0

0.005

0.01

qx

qz

1

2

5

β

ϕ

1’

2’3’

3

4

w

2q

33--D D LineshapeLineshape from Sample Rotationfrom Sample Rotation


qx

qz

rectangle

qx

qz

trapezoid

qx

qy

qz

ω

2θdiffraction axis

Q

20

10

0

-10

Rotation Angle (deg)

0.30.20.10.0

qx (Relative to Diffraction Axis) (nm-1)

15

10

5

0

3002001000

qx

rectangle

ω

20

10

0

-10

Rotation Angle (deg)

0.30.20.10.0


15

10

5

0

3002001000

qx

ω

trapezoid

Model Transformed Raw Data

30

20

10

0

-10

-20

Rotation A

ngle (deg)

0.50.40.30.20.10.0


50

40

30

20

10

0

6005004003002001000


0.2

0.1

0.0

-0.1

-0.2

qz (Relative to Sam

ple) (nm-1)

0.50.40.30.20.10.0qx (Relative to Sample) (nm-1)

100

80

60

40

20

0

6005004003002001000ULSI, Richardson, TX

March 18, 2005

CDCD--SAXS: Pattern Cross SectionSAXS: Pattern Cross Section

β qx

qz

h

qx

qz β

Fourier transform2π/h

real space


Summary: Cross section measurement-

1. Pitch – periodicity along qx at qz =0

2. Line width – intensity modulation along qx at qz =0

3. Line height – periodicity along qz at a fixed qx

4. Sidewall angle


Photoresist Patterns Photoresist Patterns

Data measured on 5Data measured on 5--ID SAXS (DNDID SAXS (DND--CAT)CAT)Advanced Photon Source, Argonne National LabAdvanced Photon Source, Argonne National Lab

Data collection and analysis performed byData collection and analysis performed byRon Jones, Tengjiao Hu, WenRon Jones, Tengjiao Hu, Wen--li Wuli WuBeamline Scientists: Steve Weigand, John QuintanaBeamline Scientists: Steve Weigand, John QuintanaSamples: provided by Samples: provided by QinghuanQinghuan Lin (IBM T.J. Watson Research)Lin (IBM T.J. Watson Research)

Sample List:Sample List:1) IBM DOF m2 1) IBM DOF m2 -- 248nm PR, 248nm PR, --0.2micron Depth of Focus0.2micron Depth of Focus2) IBM DOF p0 2) IBM DOF p0 -- 248nm PR, “Optimal” Depth of Focus248nm PR, “Optimal” Depth of Focus3) IBM DOF p2 3) IBM DOF p2 -- 248nm PR, +0.2micron Depth of Focus248nm PR, +0.2micron Depth of Focus4) IBM DOF p4 4) IBM DOF p4 -- 248nm PR, +0.4micron Depth of Focus248nm PR, +0.4micron Depth of Focus


150nm L/S Patterns Through FocusImages provided by Q. Lin

Top Down

Cross-section

-0.2 um0.0 um+0.2 um+0.4 um

Wafer: EPPX


IBM DOF p4IBM DOF p4+0.4 micron+0.4 micron

Period = 330.5 nm +/Period = 330.5 nm +/-- 0.5 nm0.5 nmLinewidth = 160 +/Linewidth = 160 +/-- 1 nm1 nmHeight = 460 +/Height = 460 +/-- 10 nm10 nmSidewall Angle = 5.6 +/Sidewall Angle = 5.6 +/-- 0.5 deg0.5 degRandom Deviation = 5 nmRandom Deviation = 5 nm

20

10

0

-10

Rotation A

ngle (º)

0.50.40.30.20.10.0


30

20

10

0

6005004003002001000

0.15

0.10

0.05

0.00

-0.05

-0.10

-0.15

qz (Relative to Sam

ple) (nm-1)


60

40

20

0

6005004003002001000



Period = 330.5 nm +/Period = 330.5 nm +/-- 0.5 nm0.5 nmLinewidth = 160 +/Linewidth = 160 +/-- 1 nm1 nmHeight = 460 +/Height = 460 +/-- 10 nm10 nmSidewall Angle = 5.6 +/Sidewall Angle = 5.6 +/-- 0.5 deg0.5 degRandom Deviation = 5 nm

20

10

0

-10

Rotation A

ngle (º)

0.50.40.30.20.10.0


30

20

10

0

6005004003002001000

Experimental DataExperimental Data

Random Deviation = 5 nm


2

4

68

103

2

4

68

104

Inte

nsity

(cm

-1)

20151050-5-10-15Rotation Angle (º)

102

103

104

105

106

107

Inte

nsity

0.500.450.400.350.300.250.200.150.100.050.00

qx (nm-1)

20

10

0

-10R

otation Angle (deg)

0.50.40.30.20.10.0


30

20

10

0

6005004003002001000

Trapezoid ModelTrapezoid Model


Period = 330.5 nm +/Period = 330.5 nm +/-- 0.5 nm0.5 nmLinewidth = 148Linewidth = 148Height = 550 Height = 550 Sidewall Angle = 2 +/Sidewall Angle = 2 +/-- 0.3 deg0.3 deg

-20

-10

0

10

20

Rotation A

ngle (º)

0.50.40.30.20.10.0


30

20

10

0

6005004003002001000

0.15

0.10

0.05

0.00

-0.05

-0.10

-0.15

qz (Relative to Sam

ple) (nm-1)


60

40

20

0

6005004003002001000



Period = 330.5 nm +/Period = 330.5 nm +/-- 0.5 nm0.5 nmLinewidth = 148 +/Linewidth = 148 +/-- 11Height = 550 +/Height = 550 +/-- 1010Sidewall Angle = 2 +/Sidewall Angle = 2 +/-- 0.5 deg

20

10

0

-10

Rotation A

ngle (º)

0.50.40.30.20.10.0


30

20

10

0

6005004003002001000

Experimental data spread more evenly across 2-D plane than model


0.5 deg


102

2

46

103

2

46

104

2

Inte

nsity

(cm

-1)


102

103

104

105

106

107In

tens

ity

0.500.450.400.350.300.250.200.150.100.050.00

qx (nm-1)

20

10

0

-10R

otation Angle (deg)

0.50.40.30.20.10.0


30

20

10

0

6005004003002001000


Missing peaks possibly due to footer


Period = 330.5 nm +/Period = 330.5 nm +/-- 0.5 nm0.5 nmLinewidth = 153 +/Linewidth = 153 +/-- 11Height = 605 +/Height = 605 +/-- 1010Sidewall Angle = 2 +/Sidewall Angle = 2 +/-- 0.5 deg0.5 deg

0.15

0.10

0.05

0.00

-0.05

-0.10

-0.15

qz (Relative to Sam

ple) (nm-1)


60

40

20

0

6005004003002001000

20

10

0

-10

Rotation A

ngle (º)

0.50.40.30.20.10.0


30

20

10

0

6005004003002001000

Possible evidence of small standing wave effect



Period = 330.5 nm +/Period = 330.5 nm +/-- 0.5 nm0.5 nmLinewidth = 153 +/Linewidth = 153 +/-- 11Height = 605 +/Height = 605 +/-- 10 nm10 nmSidewall Angle = 2 +/Sidewall Angle = 2 +/-- 0.5 deg

20

10

0

-10

Rotation A

ngle (º)

0.50.40.30.20.10.0


30

20

10

0

6005004003002001000


0.5 deg


102

103

104

105

106

107

Inte

nsity

0.500.450.400.350.300.250.200.150.100.050.00

qx (nm-1)

2

46

103

2

46

104

2

4

Inte

nsity

(cm

-1)


20

10

0

-10R

otation Angle (deg)

0.50.40.30.20.10.0


30

20

10

0

6005004003002001000


More Complicated Structures


• Introduction


•Measurement of side wall angle & height


•Conclusions


Line roughness probed by CD-SAXS includes both side wall and top surface, this is different from LER by SEM


photoresist patterns


LER by CD-SAXS

SEM micrograph

Fourier transfer of the above


CDCD--SAXS: New Metrology for LER and CDSAXS: New Metrology for LER and CD

Low “LER”:

• > 40 orders of diffraction• Peaks isotropic


Large “LER”:

• Photoresist with (3 to 5) nm RMS sidewall roughness (1 σ)• Peaks intensities decay more rapidly (20 orders observed)• Broadened diffraction peak widths • Diffuse “halo” around beam center• “Streaks” perpendicular to diffraction axis

Sidewall Correlations: High vs. Low LERSidewall Correlations: High vs. Low LER

Low LER Grating

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

0 0.002 0.004 0.006 0.008 0.01

qy (A-1)

Inte

nsity

(nor

mal

ized

)

Low LERHigher LER


qy Higher LER Grating

Samples with more defects demonstrate higher intensity “streaking”

Extracting the “Streaks” along Extracting the “Streaks” along qqyy


1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

0 0.0005 0.001 0.0015 0.002

q (A-1)

Inte

nsity

(Arb

. Uni

ts)

1st Order

2nd Order

4th Order

Note: Intensities shifted vertically for clarityqy Photoresist 120 nm 1:1

Red Data q = qx

Black Data q = qy

qx

1st 2nd 4th

Streaks decay with increasing qxDiffraction peaks become isotropic at high qx

SAXS characterization technique• Line-edge roughness

ASin(2πνy+ϕ)

x

y


CDCD--SAXS: a model LER SAXS: a model LER –– single sine wavesingle sine wave

-0.004 -0.002 0.000 0.002 0.004

-0.004

-0.002

0.000

0.002

0.004

Kx

Ky


SAXS characterization technique


Dependence of satellite peak intensity

10 10010-4

10-3

10-2

10-1

2.0

0th order1st order2nd order

I sate

llite /

I Bra

gg p

eak

Amplitude( )( ) [ ]))()()(4()(

)(2 22

2

2

2

2

2)12(

νδνδδ −+−∆++⎥⎥⎦

⎤

⎢⎢⎣

⎡

⎥⎥⎦

⎤

⎢⎢⎣

⎡=

+

yyxyx

Wq

Dq

DqN

qqDqAqq

Sin

Sin

Sin x

x

x

I

Line roughness of copper interconnect


Probing Cu InterconnectsProbing Cu Interconnects

160 nm 1:1 120 nm 1:1

Sample: Cu filled Silicon Oxide lines

Effects demonstrated previously are magnified

Higher density of defects ??

Higher x-ray contrast


Measuring pattern quality: the diffuse “Measuring pattern quality: the diffuse “halohalo””

0

200

400

600

800

1000

1200

1400

1600

0.002 0.003 0.004 0.005q (A-1)

Inte

nsity

(arb

.)

Low LER OxideHigh LER PhotoresistHigh LER OxideEmpty Beam

Intensity integrated +/- 45 deg normal to diffraction axis


CDCD--SAXS: Measuring CD and PitchSAXS: Measuring CD and Pitch

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

0 0.01 0.02

q (A-1)

Inte

nsity

(cm

-1)

q

Basic Model:

•Simple Rectangular Profile

•Pitch determined from period of diffraction peaks

•Line width determined from relative intensities

•Decay of intensities fit with Debye-Waller factor

•Peak profiles fit with Voigt function

Data fitting performed rapidly due to simplicity of modeling anddata analysis procedures (I.e. no libraries of solutions required)


Observable defects in SAXS patterns

Fourier space Real space

•Strikes along qy direction

•Amorphous halo

•Debye-Waller factor

•Side wall & top surface roughness

•Mass fluctuations along each line

•Position fluctuation of the center of each lines


ConclusionsConclusions

• Methodology for pitch, line width, side wall angle is in place, detail cross sectional modeling is within reach

• Methodology for line surface roughness, linear mass fluctuation and center position fluctuation is in research stage


Conclusions (cont.)

•The wavelength of the probing x-ray beam can be calibrated with great precision; there is no need to calibrate the resulting dimensions from x-ray measurements

•A potential laboratory based metrology complementary to SEM, AFM and optical scattometry


AcknowledgementsAcknowledgements

•X-ray measurements were conducted at Advanced Photon Source of Argonne National Laboratory

•Test samples obtained from Intel, IBM, ISMT & Shipley (now Rohm Haas)


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Small Angle X-ray Scattering Metrology for Sidewall Angle and

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