Trends in the Backend for Semiconductor Wafer Inspection

2008 Trends in the Back-end Rajiv Roy

Rudolph tools for back-end
Use of inspection for automotive semiconductor
Investment in 100% outgoing inspection – Zero Defects
PMI correlation – Tool Correlation – Certification wafer
Test floor
Preventing probe card damage
Inspection of CMOS sensors and TSV
Micro bump / pillar bump
Through silicon stacking interconnect – New Technology
Flip-chip – advanced bumps – Transition from conventional packaging
Probe card analysis and test - Darren James presentation
Agenda

Rudolph - Where We Play – Tools for Back-End Inspection Metrology Analysis Global Support August - NSX RVSI - WS API - PrVX4

Use of Inspection for Automotive Semiconductor Investment in 100% Outgoing inspection – Zero Defects

Zero Defects and Automotive Semiconductor Industry Şafak Keçeci Infineon Regensburg June 12, 2007 Regensburg - Rudolph‘s European Yield Forum

Key Enablers of Zero Defects Program
Inspection
Automated over manual
Upstream, inline and focus on reliability -related defects
Tool stability
Operation overtime
Matching performance between tools

Zero Defect as Key for Infineon Future Customer Return Rate Status April 2006 Products with 0 ppm: Increase to … %

Inspections in the Back-end for Automotive Typical Products Available Q2 ‘09 Available today NSX with ultra-thin wafer handling Process Point Type of Inspection Handling type Outgoing Fab QA 100% 2X, 3X wafer defect Whole wafer Post-backside metallization Backside of the wafer inspection for evaporation and metal defects Ultra-thin wafer (~100u thick) handling with flipper Post-Test 100% 5X PMI Ultra-thin wafer handling Post-saw 100% 5x Film-frame handling

Use of Inspection for Automotive Semiconductor PMI (Probe Mark Inspection) Tool Correlation Certification wafer

T2T correlation and repeatability study was performed using PMI metrology data at customer site
Tool Type: NSX115 with Basler Camera
Wafer was chosen and eight bond pads were sampled for probe mark inspection.
The product setup was created on RU02 and copied over to RU01 without detector training.
The wafer was inspected 15 times on each tool. Each time, PMI raw data report was generated and saved.
The inspection was performed using 5X objective.
PMI Tool-to-Tool Correlation at Customer Site DOE Overview

Spec components tighter–camera, lenses, illumination
Illumination matching, flat-fielding, Image distortion correction
Re-do our system manufacturing build procedure
Put a “golden tool” in class 10 clean-room
Implement a “golden wafer” or a standard wafer design.
Certify new standard wafers
Certify all tools relative to “golden tool”
What did Rudolph do to Enable Tool Matching?
If your inspection tool supplier does not have
Tools designed ground up for tool matching
Standard Wafer and the concept of Golden Tool in manufacturing
Manufacturing methodologies – stringent key component quality along with tool certification procedures
You do not have an inspection tool for automotive applications

Sample Plan Bondpad 1 Bondpad 2 Bondpad 3 Bondpad 4 Bondpad 5 Bondpad 6 Bondpad 7 Bondpad 8

Left Edge Proximity ( µm ) Results

Average Left Edge Proximity ( µm ) Results Average correlation between two tools running the same wafer >96% for bond pad edge proximity

Probe Mark Area ( µm ²) Results

Average Probe Mark Area ( µm ²) Results Average correlation between two tools running the same wafer >93% for probe mark area

Automotive industry requires a metrology approach to inspection
Tools have to be designed ground up for tool matching
Must implement Standard Wafer and the concept of Golden Tool in manufacturing
Implement manufacturing methodologies – stringent key component quality along with tool certification procedures
Using a single recipe, defects with >90% correlation between tools is achievable
PMI for Automotive Products Conclusions

Test Floor Avoiding Damage to Probe Cards Detecting Tall Particles

Laser Dark-field on NSX was used to detect particles
Customer Supplied Rudolph Technologies with 2 – 300mm for inspection, with the focus of the inspection being Partial Die on the Edge of the Wafer
Inspection performed before probing to detect particles that could damage probe cards
Target Defect Size is 100µm and greater
Inspection setup
Inspection performed with 100% laser dark-field
No bright-field illumination
1x Inspection used the die size of the wafer
5x Inspection performed as barelanket wafer
Tall Particle Detection Applications Study

Laser Dark-field
With Laser Dark-field, the laser light hits the surface at an oblique angle
Only light scattered normal to the surface is captured in the optics, since the optics are normal to the surface
Defects that are large and angular (Particles, Large and Deep Scratches) Reflect More Light Normal to the Surface
Inspection Setup and Explanation Optics Incident Laser Light Particle

Images at 10X, Brightfield used only for image capture
Red in images is laser reflecting off feature
Particles detected using Laser Dark-field

Defect Height Estimates 1 2 3 4 5 6 7
Measure defect height with focus – focus on wafer surface and then focus on defect top.
15 defects were measured

Defect Height Estimates 8 9 10 11

Defect Height Estimates 12 13 14 15

The use of laser dark-field will adequately detect tall particles
The throughput will be effected by an extra dark-field pass
The 2D defect size correlates fairly well with the expected height of the particle
Using blank wafer inspection techniques, the entire surface of the wafer can be inspected for tall particles including the streets and edges of the wafer where there is no pattern
Conclusions

Inspection of CMOS Sensors & TSV

Inspect glue dimensions of bubbles after adhesion
Glass is pressed onto the silicon and the bubble size indicates the gap
If bubbles are too small, then glass is too high. If the bubbles are too big, then the glass has been pressed too low
2x or 5x inspection mag depending on precision needed
Bonding Control of glass Inspect vias for insufficient and excess glue

5x inspection mag used to inspect bottom side of the wafer and pixel area in one pass through the glass
Inspection of Bottom side of CMOS Sensor Inspect sensor array and bottom side of glass carrier in single pass Bump Pads Via

The NSX is used at 3 different stages of the CMOS sensor assembly
Customer is performing 100% inspection
Using multiple tools with tool matching (recipe sharing)
All inspections at 5x
Bumped CMOS Imager based on TSV Inspect bumps, RDL, voids and damage to RDL

Micro Bump Through Silicon Stacking Interconnect Flip-chip

Pillar Bumps come in various shapes and sizes
Height can vary from 5um to over 100um and diameter can vary from 20um to more
They can have solder cap or not
Typical applications include microprocessor, memory, etc.
Copper Pillar Bump With Solder Cap Without Solder Cap CU - Pillar Bumps

Typical height is 20-30um
Typical Pitch is 50um
Due to small size of the bump and tight pitch number of I/Os have significantly increased on a die
Interconnection of choice for most TSV packages
Micro Solder Bumps

Critical Issues and Inspection Requirements Bump Dimensions / Bump Defects Bump Height Coplanarity: Best Fit Plane Method Coplanarity: Seating Plane Method Diameter Bridge Bump Missing Bump

Critical Issues and Inspection Requirements Macro Defects
Macro Defects can found the Surface of the wafer, Traces, Bumps and Pads
Examples include, defects like a ring, fiber in bump, faint small scratch, small on bump top

Copper Pillar Bumps
Large Bump height variation requires sensor technology to be able to handle bumps from 5um to over 100um
Sensor technology should allow production throughput while maintaining measurement precision
Technology is still evolving and ultimate inspection system needs to provide flexibility for current and future requirements
Micro Solder Bumps
Small nature of the bump (25um avg. height) requires high resolution sensor as compared to the requirements for standard solder bumps
Large number of bumps and tight Pitch require high resolution sensor and large memory for data processing
Number of bumps could be over 10,000/dies and 9,000,000/wafer
Both Bump types require combination 3D and 2D inspection
Inspection Challenges

Rudolph’s Approach to Micro Bump Inspection and Metrology

For 2D Inspection - TDI Line Scan Camera
Surface Defect Inspection
2D Bump Metrology
2D Bump Defect
For 3D Inspection - Line Scan Laser
Bump Coplanarity
Bump Height
Dual Sensor Technology for Optimal Performance and Inspection Flexibility

Rudolph’s 3D Line Scan Laser with Micromap Technology
4 MHz scanning rate
1.2mm or 0.6mm Swath
Up to 200, 3D data points
Programmable spacing of data points for optimal accuracy and throughput balance
3D Laser Technology for 3D Measurements DETECTOR LASER FOCUSING LENS 200 - 400  m 1.2 or .6 mm swath

Sample Inspection Case Studies

3D Scan of Copper Pillar Bumps Raw 3D Data

3D Scan of Copper Pillar Bumps Raw 3D Data
Cross section of some bumps on a die
Dark is lower pixels of 3D scan, yellow are tallest
Damaged Bump Height Good Bump Height

Sample Wafer Height Variation Across the Wafer Avg. Dia.= 26.6um Min. Dia.= 21.6um Max. Dia.= 35um Sigma = 2.8um Avg. Height = 18.7um Min. Height = 10.6um Max. Height = 30.14um Sigma = 4.0um

Copper Pillar Bump Repeatability Results WS Mean (15 Runs at 5 runs/Day) WS STDV (15 Runs at 5 runs/Day) Bump Height Average / Die - Min 24.42 0.0085 Bump Height Average / Die - Max 27.92 0.0147 Bump Height wafer - Min 23.00 0.0246 Bump Height wafer - Max 33.91 0.0451 Wafer Height Mean 25.31 0.0088 Wafer Height Stddev 1.13 0.0021

3D scan of a Die with Micro Solder Bumps Raw 3D Data Bump Height

Micro Solder Bump Repeatability Results Measurement Avg. (um) Min. (um) (col., row) Max. (um) (Col, row) 3 Sigma (um) True X Position -3.63 -17.91 (2, 12) 13.4 (13, 12) 0.48 True Y Position 1.41 -0.45 (2, 12) 3.8 (12, 12) 0.62 True Radial Position 5.81 0.2 (3, 12) 17.96 (2, 12) 0.51 Height 13.37 10.12 (2, 12) 17.86 (13, 12) 0.53 Diameter 31.36 27.63 (8, 4) 34.27 (13, 12) 0.75

Sample Captured Macro Defects

Throughputs
Case 1
Throughput with handling based on 25 wafers/slot with 2.5X lens (2.8um pixel). Bump heights ~25um (different die-size and bump count)
100% 3D – 11.0 - 12.7 WPH
100% 3D/2D – 7.4 - 8.2 WPH

Case 2
Throughput with handling based on 25 wafers/slot with 2.5X lens (2.8um pixel). Bump heights ~40um (different die-size and bump count 100% 3D
100% 3D - 11.8 WPH
Bump count / wafer range approx 500,000 to 3 million

Conclusion of Microbump Inspection and Metrology
Copper Pillar bumps and Micro bumps require high precision sensor both for 3D and 2D measurements
Combination 2D/3D system is ideal for improved CoO
Laser is well capable of inspecting varying bump heights and providing needed precision at production worthy throughput

Conclusions and Observations of Trends
Use of Inspection for Automotive Semiconductor is increasing – it is essential component of Zero Defect Program
Inspection tools have to be designed ground up for Tool correlation including certification wafer program
Test Floors want to prevent damage to expensive probe cards because of tall particles. Rudolph offers a fast 2D solution for screening
Inspection of CMOS Sensors and TSV devices is already entering production. High throughput systems like NSX are being used currently
Micro Bump / Pillar Bump is inspected at production speeds by leading edge semiconductor manufacturers with very high accuracy and repeatability
Probe Card Analysis and Test insights will be provided in Darren James presentation

Thank you!

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Trends in the Backend for Semiconductor Wafer Inspection

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