FIB Voltage Contrast for Failure Localisation on CMOS Circuits an Overview

Transcription

1 for Failure Localisation on CMOS Circuits an Overview 8th European FIB User Group Meeting Zürich 2004 Dr. rer. nat. Rüdiger Rosenkranz Infineon Technologies Dresden Physical Failure Analysis Page 1 Never stop thinking.

2 for Failure Localisation on CMOS Circuits an Overview Introduction Basic Principles of VC Generation Basic Applications of VC Advanced Mechanisms of VC Generation 5 Advanced Applications of VC 6 7 Active Voltage Contrast with Microprobing in FIB/SEM Summary Page 2

3 1. Introduction Page 3 In FIB Images various VC Phenomena can be observed. Knowledge of the mechanisms behind it can be very benficial in failure localisation process.

4 for Failure Localisation on CMOS Circuits an Overview 1 Introduction 2 3 Basic Principles of VC Generation Basic Applications of VC 4 Advanced Mechanisms of VC Generation 5 Advanced Applications of VC 6 7 Active Voltage Contrast with Microprobing in FIB/SEM Microprobing in FIB/SEM for Failure Localisation 8 Summary Page 4

5 2. Basic Principles of VC Generation Contrast generation Ion beam Ion beam Floating structure Grounded Structure Insulated structures are charging up positively. The majority of produced secondary electrons are prevented from leaving the sample by the electric field. These structures appear dark in the image. Grounded structures do not charge and appear bright because of the high secondary electron yield. Page 5

6 2. Basic Principles of VC Generation Contrast generation Ion beam gone Level of deprocessing Floating structure Structures can be made floating by deprocessing Page 6

7 2. Basic Principles of VC Generation Contrast generation Ion beam Ion beam FIB-cut & metal deposition metal oxide silicon Structures can be grounded by FIB cutting and FIB metal deposition Page 7

8 2. Basic Principles of VC Generation Contrast generation grounded = bright structures a priori FIB connecting Applications open well contacts or metal connected to them to find opens in contact chains floating = dark structures a priori deprocessing FIB cutting Applications contact chain test structures Deep Trench: finding dielectric leakage on shortloops Finding metallisation shorts in test structures Page 8

9 for Failure Localisation on CMOS Circuits an Overview 1 Introduction 2 Basic Principles of VC Generation 3 4 Basic Applications of VC Advanced Mechanisms of VC Generation 5 Advanced Applications of VC 6 7 Active Voltage Contrast with Microprobing in FIB/SEM Microprobing in FIB/SEM for Failure Localisation 8 Summary Page 9

10 3. Basic Applications of VC Case Study 1: Metallisation shorts in comb-serpentine structure FIB cuts Page 10

11 3. Basic Applications of VC Case Study 2: opens in contact chains Page 11

12 3. Basic Applications of VC Case Study 3: Deep Trench Leakage on a shortloop wafer Page 12

13 for Failure Localisation on CMOS Circuits an Overview 1 Introduction 2 Basic Principles of VC Generation 3 Basic Applications of VC 4 Advanced Mechanisms of VC Generation 5 Advanced Applications of VC 6 Active Voltage Contrast with Microprobing in FIB/SEM 7 Summary Page 13

14 4. Advanced Mechanisms of VC Generation When diodes and transistors are involved VC generation and interpretation is much more complicated. e.g. Doping Capacitance Transistors Page 14

15 4. Advanced Mechanisms of VC Generation Doping Ion beam Ion beam Oxide Oxide Tungsten Tungsten P-well N + N-well P + Page 15 Open contacts and backward biased diodes are charging up positively.they appear dark. In contrast, forward biased diodes are bright.

16 4. Advanced Mechanisms of VC Generation Doping Ion beam Ion beam Oxide Oxide Tungsten Tungsten P-well P + N-well N + Well contacts appear always bright Page 16

17 4. Advanced Mechanisms of VC Generation Doping P-diffusion N-diffusion P-well bright dark N-well bright bright Page 17

18 4. Advanced Mechanisms of VC Generation Capacitance Ion beam Ion beam Page 18 Structures with small capacitances appear dark. Charging of large capacitors during the quick ion beam scan is hard to achieve.

19 4. Advanced Mechanisms of VC Generation Capacitance Page 19 Bitlines of low capacitance are charged during scan Capacitance VC: high low bright dark

20 4. Advanced Mechanisms of VC Generation Doping P-diffusion N-diffusion P-well bright dark N-well bright bright Capacitance Capacitance VC: high bright low dark Page 20

21 4. Advanced Mechanisms of VC Generation VC in Contact level of a DRAM Wordline decoder Dark and bright contacts can be explained by design interpretation. Gate-contacts n-well-contacts p-cont. in n-well Gate-contacts n-cont. in p-well p-well-contacts n-cont. in p-well Gate-contacts n-well-contacts Page 21

22 4. Advanced Mechanisms of VC Generation n-mos transistors P-well N + N + P-well N + N + S/D contacts (p in n-well) should appear dark but appear dark only, when gate is closed (= grounded) S/D contacts appear bright, when gate is opened (=positively charged) and structure behind gate is grounded Page 22

23 4. Advanced Mechanisms of VC Generation Overview a priori grounded grounded by FIB connecting a priori floating floating by deprocessing floating by FIB cutting bright bright dark dark dark p-diffusion n-diffusion n-diffusion next to an open gate p-well bright dark bright n-well bright bright bright capacitance high low Page 23 VC: bright dark

24 for Failure Localisation on CMOS Circuits an Overview 1 Introduction 2 Basic Principles of VC Generation 3 Basic Applications of VC 4 Advanced Mechanisms of VC Generation 5 Advanced Applications of VC 6 Active Voltage Contrast with Microprobing in FIB/SEM 7 Summary Page 24

25 5. Advanced Applications of VC Case Study 1: Bitline-contact to gate shorts in DRAM arrays Contacts appear bright, when gate is open (=positively charged) Contacts appear dark, when gate is closed (=grounded or uncharged) Leakage path Leakage path n + p - Isolation Collar n - Burried Plate Page 25

26 5. Advanced Applications of VC Case Study 1: Bitline-contact to gate shorts in DRAM arrays Contacts appear bright, when gate is open (=positively charged) Contacts appear dark, when gate is closed (=grounded or uncharged) Contacts appear bright, when they are shorted to the grounded GC (CB-GC short) bright dark dark dark CB-GC short Page 26

27 5. Advanced Applications of VC Case Study 1: Bitline-contact to gate shorts in DRAM arrays By FIB grounding of GC lines CBs can be made to appear dark, except those which are shorted to grounded GCs. Page 27 Image: Martina Kuhnert, Infineon Dresden

28 5. Advanced Applications of VC Case Study 1: Bitline-contact to gate shorts in DRAM arrays Page 28 Marking of a single CB-GC short Image: Ruby Harzer, Infineon Dresden

29 5. Advanced Applications of VC Case Study 2: open BL contacts Page 29 Images: Corina Buhl, Infineon Dresden

30 5. Advanced Applications of VC U c R high I s Influence of leakage current dark U c t R medium I s grey U c bright t floating structures structures with little leakage structures grounded R low I s dark grey bright Page 30 t

31 5. Advanced Applications of VC Case Study 3: Gate contact opens C1 contacts connected via CG to gate C1 M0 CG C1 connected to a gate medium capacitance Gate C1 M0 CG Page 31 Image: Corina Buhl, Infineon Dresden C1 not connected to a gate small capacitance Gate

32 5. Advanced Applications of VC Case Study 3: Gate contact opens CG not etched properly Page 32 Image: Corina Buhl, Infineon Dresden

33 5. Advanced Applications of VC U c Influence of structure capacitance RI s dark grey bright high Capacitance med. Capacitance low Capacitance t scan t structures with low capacitance dark structures with medium capacitance grey structures with high capacitance bright Page 33

34 for Failure Localisation on CMOS Circuits an Overview 1 Introduction 2 Basic Principles of VC Generation 3 Basic Applications of VC 4 Advanced Mechanisms of VC Generation 5 Advanced Applications of VC 6 Active Voltage Contrast with Microprobing in FIB/SEM 8 Summary Page 34

35 6. Active Voltage Contrast with Microprobing Page 35 Kammrath&Weiß 4-Prober Modul

36 6. Active Voltage Contrast with Microprobing Kammrath&Weiß 4-Prober Modul in FEI DB 235 Page 36

37 6. Active Voltage Contrast with Microprobing Overview Pad to pwell ROI Page 37

38 6. Active Voltage Contrast with Microprobing 0V Page 38

39 6. Active Voltage Contrast with Microprobing +2V Page 39

40 6. Active Voltage Contrast with Microprobing -4V Page 40

41 6. Active Voltage Contrast with Microprobing -4V Detail In the area where GC is connected to the substrate, CBs show an inverted VC, when pwell is on 4V. -4V Page 41

42 7. Summary 1 can help to find failures in CMOS circuits, where electrical failure analysis can t. 2 is a supplementary method for electrical failure analysis. 3 Successful VC failure localisation in cases where devices are involved requires a good knowledge of layout. 4 Active Voltage Contrast is a promising methode. Page 42