CMP Scratches; Their Detection and Analysis on Root Causes

Transcription

1 6 th LEVITRONIX CMP and Ultrapure Conference The Westin Park Central, Dallas, Texas May 11-12, 2011 CMP Scratches; Their Detection and Analysis on Root Causes Jin-Goo Park May 11, 2011 Department of Materials Engineering, Hanyang University, Ansan, , Korea

2 Outline Introduction Issues of CMP Defects(Scratch) Motivation Experimental Lab. capability Experiment tools & procedure Results Post-CMP cleaning Detection method of scratches Scratch source & scratch shape (pad debris, dry particle, diamond particle) Effect of Large Particle concentration Effect of conditioner diamond Summary 6 th LEVITRONIX CMP and Ultrapure Conference 2

3 ICPT 2011 in Seoul, Korea November 9 11, 2011 Abstract due online July 4, th LEVITRONIX CMP and Ultrapure Conference 3

4 Scratch Sources in Oxide CMP Slurry Pressure Conditioner Surface Wafer Head Slurry Conditioner Polishing pad Polishing table Pad Surface CMP consumables : Pad, Slurry, Conditioner These consumables should be controlled to achieve better performance 6 th LEVITRONIX CMP and Ultrapure Conference 4

5 The Migration of CMP Technology Polishing recipe Pressure control & table speed tuning CMP Tool Chosen the tool equipped the head of retainer ring and membrane Pattern design Removal profile control Slurry Applied optional slurry for each process AMAT MIRRA tool CMP simulation & dummy pattern insert Consumable part Compounding the consumable parts Removal profile & selectivity, dishing control The alterative application of consumable parts 6 th LEVITRONIX CMP and Ultrapure Conference 5

6 The Type of defects Produced after oxide CMP Surface Void Residual Slurry Common CMP Defects Surface Particle Embedded Particle Scratch Scratch is the most deleterious defect compared to other type of defects. 6 th LEVITRONIX CMP and Ultrapure Conference 6

7 ITRS Roadmap Micro-scratches and defects can lead to severe circuit failure, low yield and potential reliability issue. It is important to evaluate defects and their sources for CMP sustainability. Among defects, scratch is still not well understood in CMP process 6 th LEVITRONIX CMP and Ultrapure Conference 7

8 The Factors that Play Key Role in the Scratch formation Wafer Surface Wafer hardness : TEOS, HDP, BPSG Film Material : Cu, STI, ILD Slurry Abrasive size and Distribution Large particle concentration Abrasive type (Colloidal, Fumed, New type) and Agglomeration Particle morphology Pad Design (asperities, pore and groove) Hardness Conditioner 6 th LEVITRONIX CMP and Ultrapure Conference Diamond size & density Diamond shape Diamond patterns Role of Active diamond Diamond wearing or breaking Pad asperity& contact area Pad profile Pad debris Pad cutting rate 8

9 Motivation Effect of CMP process and consumables Detection of scratches formed on oxide wafer To evaluate the post CMP cleaning process to detect the scratches easily by a new technique CMP Process (pressure, velocity of head/platen) CMP performance Study on Scratch formation CMP Slurry CMP pad & conditioner Thin film materials 6 th LEVITRONIX CMP and Ultrapure Conference 9

10 Experimental (Modification of Polisher Head) DOOPLA310 (300 mm) 12 Head 8 Head (scratch test) Modification and Installation of 8 polisher head for scratch formation and detection 6 th LEVITRONIX CMP and Ultrapure Conference 10

11 Experimental Procedure (Scratch Formation) Repeating New Pad Break-In Conditioning CMP -Dummy (2) - RR&N.U (2) - Gathering (2) -- Scratch (3) Cleaning Detection Pad IC1010 Break In - Conditioning with DIW (30min) - Conditioning with Slurry (10min) Conditioning - Conditioning with DIW (10min), - Conditioning with Slurry (5min) CMP - Dummy CMP 2times - CMP for CMP performance 2 times - Dummy CMP for slurry gathering 2times - CMP for scratch 3times Cleaning - SC-1 (10min) Over Flower (3min) DHF (3min) Over Flower (210 Sec) SC-1 (10min) IPA Dry 6 th LEVITRONIX CMP and Ultrapure Conference 11

12 7,200 5,750 1,450 Optimization of Post-CMP Cleaning for Scratch Detection Lab. capability : Clean Room (class 10) - Post-CMP Cleaning & Scratch detection Ozone Generator Akrion Single Tool Clean Area Wet Station H2-DIW Generator Aaron Single Tool FPD Cleaning Tool Air Shower Dress Room Particle Scanner (Surfscan6200) Particle deposit ion OM Sample Room Entrance PIV Main Table Work Table table Laser Shock Wave Cleaning Tool Fluorescent Microscope Contact Angle Analyzer AFM 6 th LEVITRONIX CMP and Ultrapure Conference 12

13 Analysis Tools for Scratch detection Defect number Scratch shape Optical Microscope (Nikon, LV-100D) Particle scanner (Surfscan 6200, KLA-Tencor, USA) 1000X 20μm Surfscan6200 (KLA-Tencor) : Detection of Scratch number Control the Gain value & Threshold value Analysis of Scratch shape Counting the non-removed particle after cleaning 6 th LEVITRONIX CMP and Ultrapure Conference 13

14 LPD (ea) Post-CMP Cleaning (Role of Scrubber Cleaning) A standard, hollow cylindrical sponge with nodules PVA Scrubber Effect of Scrubber Cleaning Gain(4), Threshold(0.18) : 0.18 um ~ 1.6 um Gain(4), Threshold(0.36) : 0.36 um ~ 1.6 um Schematic of removal of particle from surface by scrubber 1 min No scrubber Scrubber Wet Send Indexer DIW Brush Module Scrubber Cleaning after slurry dipping during 1min PRE is increased by scrubber cleaning 6 th LEVITRONIX CMP and Ultrapure Conference 14

15 LPD (ea.) Optimization of RCA Cleaning (Wet station for 200/300mm wafer cleaning) Sequence : 1. SC1 2. HF Particle Size Range 0.18 ~ 0.6 um 0.21 ~ 7.7 um 0.32 ~ 28 um 2 ~ 63 um SC-1 SPM HF Sink IPA vapor dryer Initial SC-1 SC-1 => HF SC-1 Quartz bath Quartz heater Optimization of SC1 process - NH 4 OH : H 2 O 2 : DIW = 1 : 2 : 50 C with 1MHz megasonic Optimization of HF Cleaning and Etching (HF 0.5%) - HF cleaning (30s) : Particle removal - Scratch etching (180s) : Magnification of Scratch 1 MHz Megasonic Optimization of IPA vapor dryer 6 th LEVITRONIX CMP and Ultrapure Conference 15

16 Effect of HF etching for Scratch Detection Before HF etching After HF etching Treatment of HF solution (30s) - Surface cleaning Treatment of HF solution (180s) Extension of generated scratches Scratches were extended to defect easiliy by HF solution after CMP 6 th LEVITRONIX CMP and Ultrapure Conference 16

17 PRE of cleaning process and optimization of surfscan recipe Gain(1) Threshold (2 μm ) At threshold 2 μm almost all the particle were removed (Efficiency 99%) Hence any particle appear at this range after CMP process, that might be related to the scratch directly. 6 th LEVITRONIX CMP and Ultrapure Conference 17

18 Removal Rate (nm/min) CMP Performance & Scratch Number (Reference) Non-Uniformity (%) The number of scratch (EA) Removal Rate & Non-uniformity Removal Rate Non-uniformity Scratch Number (reference) 2 ~ 63 m Control the high scratch using the break-in process - 30min with DIW - 10 min with slurry The time of CMP The time of CMP Evaluation of Reference process during 360 times CMP - Process Condition : 4.5 psi, head 67rpm/ platen 73 rpm, 30s - RR : Avg. 460 nm/min, WIWNU : below 5% Evaluation of Reference Scratch formation during 360 times CMP - Reference scratch formation : below 15EA 6 th LEVITRONIX CMP and Ultrapure Conference 18

19 Scratch Detection Mathods Surface Analyzer Image Section Paper (0,0) (0,0) Both surface analyzer image and section paper exactly overlapped The surface analyzer image exactly overlapped with section paper to detect the location of the defects Each individual defect was inspected by Optical Microscope using the above approach 6 th LEVITRONIX CMP and Ultrapure Conference 19

20 Summary of Scratch Detection Method ea CMP Clean Oxide Wafer Post-CMP Cleaning 20 ea Scratch Image By Surface Particle Scanner (surfscan 6200 KLA, Tencor, USA) Lap Scale (micron) Specific Scratch at Specific Area Scratch Characterization ( Dimension, Shape) SC-1 (60 0 C, 10min) Removal of Slurry Reside SC-1 (60 0 C, 10min) DHF (0.5vol%, 210s) Extension of Scratch Marangoni IPA Dry By Optical Microscope ( LV- 100D, Nikon, Japan) 6 th LEVITRONIX CMP and Ultrapure Conference 20 Removal of Re-contamination particle Removal of Water Mark

21 Capturing the image of a scratch by the new method Wafer Matching Test after CMP um OM image um AFM image The specific scratch at specific region could be observed by a microscope using wafer matching method. Over 95% accuracy was observed in detecting the scratches And also, the scratch analysis was done by AFM 6 th LEVITRONIX CMP and Ultrapure Conference 21

22 Classification of Scratches Formed on Oxide Surface Line chatter Broken chatter Group chatter The Major type of scratch shapes are Chatter on oxide surface : Chatter type occupies more than 70% Continuous Line Broken Line Random Sliding of embedded large particle Indentation depth determine the scratch shape Irregular scratch source and it s behavior may generate the random type 6 th LEVITRONIX CMP and Ultrapure Conference 22

23 Scratch Formation Theory (Chatter Scratch Formation) Most probable mechanism Stick-Slip phenomena - Stick friction is increased by the stress concentration, which induce the Scratch formation - Slip friction is generated after surface fracture, which decide the distance between chatter scratch * H-J Kim, et al., Modeling on the CMP Scratch, 43th Technical Meeting of Korea CMPUGM (2009) 6 th LEVITRONIX CMP and Ultrapure Conference 23

24 Gathering of CMP byproducts Schematic diagram of slurry gathering system Slurry Delivery Atomizer After CMP Vacuum Pump Head Conditioner To investigate the scratch sources generated during polishing, a gathering system was developed to collect the byproducts directly during the CMP process. After examining the several locations, to gather byproducts, it was found that gathering of byproducts at the back position of the wafer would be the better position. 6 th LEVITRONIX CMP and Ultrapure Conference 24

25 SEM and EDX analysis of gathered CMP byproducts The comparison was performed among fresh pad and byproducts collected during just conditioning and actual polishing SEM images shows the presence of some large matter in byproducts EDX analysis confirms that the large matters related to pad debris. The byproducts of polishing also contains Si composition, which is due to the slurry It could be concluded that generation of pad debris is significant during CMP process and their effect should be studied. 6 th LEVITRONIX CMP and Ultrapure Conference 25

26 Number of Particle The number of Byproduct after CMP Number of Byproduct Slurry 100 L Fresh slurry In-situ conditioning Particle Size ( m) After CMP process, large particle number is increased in byproduct (byproduct 100 ul) During in-situ conditioning, Pad debris is generated which affect to scratch formation 6 th LEVITRONIX CMP and Ultrapure Conference 26

27 Scratch Number (%) Scratch Number (%) Scratch Number (%) Scratch Number (%) Correlation between scratch source and scratch shape Reference Wafer Addition of Pad Debris Line Chatter Broken Chatter Dot Chatter Group Chatter Total Chatter Continuous Line Broken Line Total Line Rolling type Addition of Dried Slurry Particles 0 Line Chatter 100 Broken Chatter Dot Chatter Group Chatter Total Chatter Continuous Line Broken Line Total Line Rolling type Addition of Diamond Particles Line Chatter Broken Chatter Dot Chatter Group Chatter Total Chatter Continuous Line Broken Line Total Line Rolling type Different scratch sources added individually to the CMP process and then their effect on scratch shapes was studied 27 6 th LEVITRONIX CMP and Ultrapure Conference 20 0 Line Chatter Broken Chatter Dot Chatter Group Chatter Total Chatter Continuous Line Broken Line Total Line Rolling type

28 Schematic of Scratch Generation Hard Surface (HDP) Soft Surface (BPSG) HDP TEOS BPSG F Pad Wafer α δ Hertzian Indentation - In oxide film, scratch is generated by particle s indentation depth and stick-slip phenomenon - In lower hardness films, assume that longer and wider chatter type was generated due to deeper indentation depth and rotation of particles. 6 th LEVITRONIX CMP and Ultrapure Conference 28

29 Effect of Conditioner Diamond Density On Scratch Formation Conditioner Images as a function of Diamond Density Conditioner #1 - Low density diamond Conditioner #2 - Mid density diamond (Std. conditioner) Conditioner #3 - High density diamond 6 th LEVITRONIX CMP and Ultrapure Conference 29

30 Removal Rate (nm/min) CMP Performance as a function of Diamond Density Non-uniformity (%) Differential number % Removal Rate & Non-uniformity After conditioning with DIW Removal Rate Non-uniformity Diamond Density Low Mid High Low Mid Diamond Density High Diameter (nm) In high density conditioner case, Lower RR (450 nm/min) is measured than that of other conditioners Conditioning with DIW - Larger pad particle is generated during high density diamond conditioning 6 th LEVITRONIX CMP and Ultrapure Conference 30

31 Pad Surface Analysis after conditioning Pad height probability (Data for *Dow chemical Company) Diamond conditioner row mid high Polishing Pad - Pad height probability is measured after conditioning - (Wyco-NT9100, VEECO, USA) After conditioning using the High density diamond conditioning, Pad height probability is generated at high pad height It means that conditioning is provided to only pad asperity area. Also, enough conditioning isn t provided at the pore area Because the pressure on each diamond of high density is lower than that of standard or low density conditioner 6 th LEVITRONIX CMP and Ultrapure Conference 31

32 The Number of Scratch (EA) Scratch Number as a function of Diamond Density 70 HF 0.5% etching (210s) Low Density Mid Density High Density - The scratch number is measured after HF 0.5 vol% etching (210s) - The highest number of scratch is generated during polishing with high density diamond conditioner - The scratch number may be affected by conditioner performance and generated Pad particle size 6 th LEVITRONIX CMP and Ultrapure Conference 32

33 Summary Optimized Post CMP Cleaning Process - Cleaning sequence : SC1 (10min) HF Cleaning (210s) SC1 (10min) wafer Dry SC1 Cleaning : Removal of particles HF Cleaning : Removal of particles and extension of scratches Classification and sub classification of scratch shapes on oxide after CMP - The major type of scratch shapes are Chatter on oxide surface - Also, unstable friction between pad and wafer may generate the Broken/Group chatter scratches Scratch Source Vs Scratch Shape - Three different scratch sources were tested on the shape of scratch formation. - It was found that specific scratch source has specific effect on scratch shape and size. - The dried and diamond particles showed severe effect on scratch formation due to their hard nature Characterization of Process Consumables - Surface hardness : Indentation depth by abrasive particle affect to scratch number and shape - LPC : Large particle of slurry can cause the unstable scratch formation - Conditioner : Conditioner performance may affect to the pad debris generation and scratch formation 6 th LEVITRONIX CMP and Ultrapure Conference 33

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