(TSV) Metrology with White Light Interference Microscopy

Through Silicon Via (TSV)Through Silicon Via (TSV) Metrology with White Light Interference MicroscopyMetrology with White Light Interference Microscopy

Erik Novak and Joanna SchmitVeeco Instrument, Inc.

Tucson, Arizona

©2009 Veeco Instruments Inc.2

Every day devices rely on high tech sensors and processors Every day devices rely on high tech sensors and processors

CMOS sensor

DRAM

Logic processor


3D Integration Will Enable Advances in Device Performance and Cost 3D Integration Will Enable Advances in Device Performance and Cost


Adoption of TSV is Expected to Accelerate Adoption of TSV is Expected to Accelerate

16% CAGR

3D Equipment: wafer bonders, chip bonders, etching-drilling, plating, lithography, deposition-coating, temporary bonding, grinding-thinning, inspection & metrology, test tools

3D materials: advanced photoresist, permanent & temp adhesives, gas, advanced substrates…

D


TSV Metrology Needs Are DiverseTSV Metrology Needs Are Diverse

Via Dimensions– Via diameters are 50um (CIS) down to 1-2um (Logic)– Via aspect ratios are typically 1:1 to 10:1

Prioritized Measurement Requirements– Depth– Top & Bottom CD– Via Pitch– Sidewall angle (top & Bottom)


Multiple Optical Methods Serve TSV Measurement Needs Multiple Optical Methods Serve TSV Measurement Needs

Infrared illumination based microscopes– “See” through silicon– Allows for alignment of stacked wafers – Poor lateral and vertical resolution due to

– Long wavelength– High measurement noise

White light confocal systems– Good lateral resolution– Lower vertical resolution for high aspect ratios– Slow vertical scans– Does not “see through silicon”

White light interferometric optical profiler– Good lateral resolution– Excellent vertical resolution even at high aspect ratio– Fast vertical scans– Mature technology, in production for decades– Does not “see through silicon”


White Light Interferometers Are Easy-to-Use But Powerful Metrology Systems

Add an specialized objective and precision scanner to an extremely stable microscope platform

Scan objective vertically through focus

CCD camera captures the sinusoidal interference pattern during the scan

Best focus is determined from signal phase and/or contrast

A 3D image is created from the best focus map

Sample

Beamsplitter

ObjectiveMirauInterferometer

Light Source

CCD

Reference signaldetector(s)

Reference signal module

Laser

Mirror on the scanner

Reference mirror

Mirror


System Rapidly Scans Through Focus for Rapid 3D Measurements

System Rapidly Scans Through Focus for Rapid 3D Measurements

VSI•Height ranges up to 10mm

•Measurement Time < 5 sec

•Vertical resolution 0.01nm


Standard WLI Profilers Provide Excellent Metrology for Vias Down to 5 µm Widths Standard WLI Profilers Provide Excellent Metrology for Vias Down to 5 µm Widths

Widthmicrons

MaxAR

TRENCH >2 10:1

VIA >5 4:1

Excellent for measurement of via:

– Depth– Top CD – Via Pitch

1 sigma variation typically < 0.05%


Narrow Features Are Challenging but Measurable with Optimized WLI Systems Narrow Features Are Challenging but Measurable with Optimized WLI Systems

Capabilities of optical profiler are increased by:

– Modified illumination

– Advanced Signal Processing

– Precise system alignments

Very Little Light Strikes The Bottom of the Via


Custom Objective Uses a Separate Illuminator to Penetrate Deep Features Custom Objective Uses a Separate Illuminator to Penetrate Deep Features

MicroscopeObjective

Sample

ReferenceMirror

Fringes in focus

Advantages of illumination from below of the objective• Collimated illuminating beam better penetrates the via• High numerical aperture of objective captures most light


Specialized Signal Processing Distinguishes Between Substrate and Via Signals Specialized Signal Processing Distinguishes Between Substrate and Via Signals

Ghost fringes in void area of via.

‘Ghost’ fringes appear on top and bottom of trenches and vias < 5um wide and may be stronger than the true signal

Narrow features cause signal from each surface to extend into other regions


System Alignment Must Be Perfect to Measure Deep Features System Alignment Must Be Perfect to Measure Deep Features

Objective

System

Lateral misalignment of optical elements

Objective

Relative tilt of objective/sample

MicroscopeObjective

Sample

ReferenceMirror

Position

Fringes below focus

Fringes in focus

•Precise alignment required in order for the light to reach the bottoms of vias and trenches.•Positions and angle of many optical elements needs to be tightly controlled•Laser is used for best performance

Light source positionTilt of the bending mirror/prismTurret lateral offset positionTilt of the objective

(may be caused by the tilt of the reference mirror)

Reference mirror alignment


TSV Enhancement Dramatically Improves Capability of White Light Optical Profiler TSV Enhancement Dramatically Improves Capability of White Light Optical Profiler

Widthmicrons

MaxAR

TRENCH 3-1 40:1

VIA 3-1.5 10:1

Widthmicrons

MaxAR

TRENCH 5-2 10:1

VIA 5 4:1

Standard Capabilities

With TSV Enhancements

Measurement Results


Narrow Trenches Up to 40:1 Aspect Ratio Can Be Measured Using Enhanced WLI systems Narrow Trenches Up to 40:1 Aspect Ratio Can Be Measured Using Enhanced WLI systems

It is easier for the light to travel inside the trench than in a via due to extended dimension in one direction

System Measurement Performance – Trenches up to 500 microns deep– 1:40 aspect ratio trenches– Fields of view from 200 µm x 300 µm to >15mm x 15mm – 4 seconds measurement time– 1 sigma repeatability <0.5%


Many Trenches Are Measured in Each Scan Many Trenches Are Measured in Each Scan

Integrated image processing automatically identifies and reports individual trench data

Average Depth: 14.3 microns (across all the lines)

Width from 1 to 10 microns

Average 1 Sigma Standard Deviation of depth: 70nm


Narrow Vias Can Also be Characterized with TSV-Enhanced WLI System Narrow Vias Can Also be Characterized with TSV-Enhanced WLI System

Lateral dimension is small in both directions: x and y so signal must be optimized

Successful Measurements: – 1.5 micron wide, 10 µm deep – 3 micron wide and 35 µm deep vias – 5 micron wide and 55 µm deep vias

– 1:15 aspect ratio vias– < 5 seconds per measurement– <0.4% 1 sigma on width and height


3 micron wide, 35 micron deep vias Heights are inverted here to show the profile 3 micron wide, 35 micron deep vias Heights are inverted here to show the profile

10 measurements, no remove/replace

3 micron vias:– Average Depth:

34.63 µm – Average width:

3.4 µm

Data is shown inverted for clarity


Vias 5um wide, 10 um pitch 55um deepVias 5um wide, 10 um pitch 55um deep

E


Veeco Has Demonstrated Capability on a Large Variety of Features Veeco Has Demonstrated Capability on a Large Variety of Features

CIS DRAM LogicLogic

(Multi-Core)Via dia (um) 5 to 50 20 to 100 5 to 20 1 to 5Thickness (um) ~ 100 20 to 75 50 to 75 20 to 50Density per wafer (k#) 40 to 300 20 to 60 200 to 1,000 1,000 to 10,000

E

Measured TSVs

0

20

40

60

80

100

120

0 5 10 15 20Wi dt h

i n mi cr ons

Dep

th in

mic

rons

Trenches 1 Trenches 2 Vias 1 Trenches 3 Sematech Vias

Current t rend Future trend M IT vias Vias 3 Trenches 4

Industry requirement by technology


Individual Feature Measurements Show High Repeatability Individual Feature Measurements Show High Repeatability

Dimensions Height 1 sigma Std Dev (µm)

Height 1 sigma Std Dev

Width 1 sigma Std Dev (µm)

Width 1 sigma Std Dev

3.4 x 35 µm via

0.10 0.4% 0.02 0.4%

3.0x10 µm via 0.02 0.2% 0.02 0.4%5.0 x 12 µm via

0.02 0.2% 0.01 0.2%

5.0 x 55 µm via

0.02 0.03% 0.01 0.2%

3x14 µm trench

0.07 0.5% 0.01 0.3%

Average results over a field of view typically 10X better

Multiple scans improve results by Sqrt(# measurements)


Enhanced WLI Provides Highly Capable TSV Measurements Enhanced WLI Provides Highly Capable TSV Measurements

Interferometry has the highest vertical resolution of any measurement technique

Visible light provides higher lateral resolution than infrared

Unlike confocal, performance is unchanged as you vary magnification/field of view

Enhanced systems measure:– Trenches of 40:1 aspect ratio, <2 µm wide – Vias of 15:1 aspect ratio, <1.5 µm wide

Systems have been in production environments for >20 years

Configurations range from table-top research systems to self-calibrating, wafer-handling systems


AcknowledgementsAcknowledgements

Samples:– Andy Rudack and Sematech

– MIT Microsystems Technologies Laboratory

Come See Veeco Instruments’ WLI Systems at– Chad Industries, Booth 5251, Semicon West– Veeco Metrology, Booth 8346, Intersolar

My e-mail: [email protected]

Documents

(TSV) Metrology with White Light Interference Microscopy