Sample Preparation Techniques (Theory & Applications)- Microsectioning Technology, Metallography

Sample Preparation Techniques (Theory & Applications)- Microsectioning Technology, Metallography

Introduction: Challenges of Microelectronic Cross-Sectioning Complexities of Modern Microelectronics Planning a Course of Action

Complexities of Modern Microelectronics Current microelectronic cross-sectioning requires us to deal with the following issues: Decreasing Feature Size Combined Materials Properties

Combined Materials Properties Microelectronics and their packaging are COMPOSITE structures. Many of the materials found in microelectronic samples have widely varying materials properties.

Comparative Description of Materials Properties Material Hardness Ductile/Brittle Silicon Moderate Brittle Gallium Arsenide Moderate Brittle Aluminium Soft Ductile Oxide Films Hard Brittle Solders Very Soft Ductile Gold Wires Very Soft Ductile Ceramic Substrates Hard Brittle Insulators Hard Brittle Tungsten Hard Ductile Ti/W Hard Ductile

Microstructure Macro - see with an unaided eye Micro - need a microscope to see Atomic the position of the atoms in the unit cell Structure - how things are put together BCC FCC

Why Microstructures are Important Characterize materials for different applications Control manufacturing processes Analyze failures

Information Observed Specimen preparation quality is the determining factor in the value of the examination.

Preparation Requirements Freedom from deformation Absence of thermal damage Flatness Freedom from scratches

Preparation Steps Each step is equally important Sampling Sectioning Mounting Grinding and Polishing Visual Examination Etching Analysis

Sectioning

Mounting - Compression Introduction

Mounting - Castable Introduction

Grinding / Polishing Introduction

Introduction Analysis Capture photos / electronic images Comparison charts Depth / thickness measurements Image analysis

Sampling Sampling Specimens selected must be representative of the material to be examined Driven by the type of the investigation Quality Control Failure Analysis Research and Development

Sectioning Sectioning Removing a specimen from a larger component Final size: typically 2 inches or less in diameter Cut plane should be as near to the desired location as possible Aggressive cutting methods will require excessive damage to be removed Re-sectioning the specimen Grinding beyond the deformation depth

Sectioning Sectioning Parameters Equipment (Abrasive cut-off, Precision saw) Blade, Wheel (SiC, Al 2 O 3, diamond) Method Load Speed Feed Rate Contact Area Coolant Note: Delicate materials may require encapsulation

Sectioning Abrasive Wheel Selection SiC wheel - nonferrous materials Al 2 O 3 wheel- ferrous materials Hard wheel / soft material Soft wheel / hard material

Sectioning Cut-off Wheel Selection Application Bond Abrasive Tool Steels 60 HRC & Above Carburized Steels Rubber resin Al 2 O 3 Hard Steel 50 HRC Rubber resin Al 2 O 3 Medium Steel 35-50 HRC Rubber resin Al 2 O 3 Soft or Annealed Steel 15-35 HRC, 46-90 HRB Rubber Al 2 O 3 Medium Hard Nonferrous Materials, Uranium, Titanium, Zirconium Soft Nonferrous Materials, Aluminum, Brass, etc. Very Hard, Brittle Fracture Materials Carbides, Ceramics, Petrographic Rubber Rubber Metal SiC SiC Diamond

Sectioning Selecting a Method MACC - Minimum Area of Contact Cutting To minimize damage Keep pressure on abrasive particles as low and constant as possible Minimize contact area between wheel and specimen

Sectioning Methods Available a -Chop b -Pulse c -Oscillation d-traverse and increment e -Orbital cutting

Sectioning Troubleshooting Problem Possible Cause Suggested Remedy Burning (bluish discoloration) Rapid wheel wear Frequent wheel breakage Resistance to cutting Overheated specimen Wheel bond breaking down too rapidly Loose specimen fixturing Uneven coolant distribution Wheel glazing Slow wheel breakdown Increase coolant rate Lighten cutting pressure Choose wheel for harder material Decrease feed rate Choose wheel for softer material Lighten cutting pressure Clamp the specimen rigidly Choose wheel for harder material Use minimal area contact cutting Choose wheel for harder material Reduce coolant flow Cutter stalls Cutter capacity inadequate Use cutter with greater Hp Limit specimen size

Sectioning Methods: Cleaving Advantages: Fast! Semiconductors and insulators break cleanly. Can be used to section an individual feature or to quickly reduce the size of a large sample.

Disadvantages Metals and polymers don t cleave well. Cleave doesn t always hit desired feature. Can only be used for bare die

Sectioning Methods: Diamond Saw Sectioning Advantages: Relatively fast. Can be used on almost any sample In most cases, can be used to trim sample close to target feature.

Disadvantages Cannot be used to produce a finished cross-section. Slow cutting through potted samples. Creates damage that must be removed.

Choosing an appropriate blade for Diamond Saw Sectioning BLADE PURPOSE 15 HC, LC General Purpose Blades for Sectioning Metals, Ceramics, Composites, etc. 10 LC Ideal for sectioning Packaged Semiconductors with mineral filled epoxy packaging, or samples with organic or ceramic substrate. 5 LC Ideal for sectioning Bare Die Semiconductors without packaging.

Why Mount Specimens? Mounting of Specimens Protect edges during polishing process Protect delicate samples Increase life of polishing surfaces Uniformity - allowing for automation Safety

Mounting of Specimens Methods Clamp Mounting Compression (Hot) Mounting Pressure Heat Castable (Cold) Mounting Resin selection Vacuum

Mounting of Specimens Method Selection Specimen characteristics to consider Brittle, Friable Heat Sensitive Porosity Level EPOMET EPOXICURE vacuum impregnated

Selecting a Mounting Compound Mounting of Specimens Phenolic (Phenocure ) Economical High Shrinkage Low Hardness Poor Edge Retention Epoxy (Epomet ) High Hardness Low Shrinkage Chemically Resistant Acrylics (Transoptic ) Transparent Slow Cure Fair Hardness Defect Prone Low Chemical Resistance

Castable Mounting Cold Mounting Acrylics Varidur Sampl-Kwick Epoxies Epo-Kwick Epoxicure Epo-Thin Epo-Color Mounting of Specimens

Castable Mounting Typical Parameters Mounting of Specimens Acrylics 5-15 min. curing; 170-175 F Epoxies 30 min. - 20 hr. curing; 80-185 F

Troubleshooting Castable Resins Variables Quantity Ambient temperature Mold type Specimen size {speaker} Incorrect mixing, mixture not homogenous Inaccurate proportioning of resin to hardener Shelf life typically is one year Specimens not fully dried Mounting of Specimens

Grinding Grinding Principles Fixed and semi-fixed abrasives surfaces SiC Ultra-Prep diamond disks BuehlerHercules (Hard and Soft) Abrasive size: 150 to 5µm Use lubricant to minimize thermal damage and remove debris from the platen

Grinding Initial Grinding Step Goals Remove the damage resulting from the sectioning process Establish a planar surface Reach a specific plane close to a desired area/feature Extent of sectioning damage determines the selection of the initial abrasive size

Grinding Subsequent Steps Remove damage from previous step(s) Decreasing abrasive size Depth of damage decreases Removal rate decreases Depth of damage is greater for soft materials than hard materials

Polishing Polishing Principles Resilient surfaces with abrasives applied Cloths: woven, pressed, napped Reveal true microstructure of the material Maintain flatness Keep artifacts to an absolute minimum

Polishing Final Polishing Principles Remove any remaining artifacts or smear Produce a lustrous, scratch-free surface Maintain edge retention as much as possible

Grinding / Polishing Abrasives SiC Polymers Metals Al 2 O 3 Ferrous based materials Diamond Metals Ceramics Composites SiO 2 Non-ferrous materials

Grinding / Polishing SiC papers Typical sequence 240 (P280) 320 (P400) 400 (P600) 600 (P1200)

Grinding / Polishing Grit Equivalency Chart USA Grit (ANSI / CAMI) European Grit (FEPA P) Approx. Size (µm) 180 180 78 240 P280 52 320 P400 34 400 P600 23 600 P1200 15 800 P1500 12 1200 P2500 7

Grinding / Polishing Diamond Monocrystalline Polycrystalline Polycrystalline shorter preparation times higher surface area on the diamond particles provides more cutting points

Grinding / Polishing Applying Diamond Abrasive Metadi Suspension Each squirt from the bottle about 1 ml Add at the beginning and then about every 30 sec. Metadi Paste Apply even across the selected surface Add Metadi fluid at the beginning and then about every 30 sec.

Grinding / Polishing Amount of Abrasive Too little cutting rate reduced Too much hydroplaning Variables Surface selected Format size: 8 vs. 10 Platen RPM Removal Rate (um/min) 30 25 20 15 10 5 0.33 ml/min 1.83 ml/min 13.83 ml/min Texmet 1000 UltraPol Hercules H Parameters: Al specimens, 9µm diamond, 150 RPM, 5 lbs/specimen, 8 format

Grinding / Polishing Final Polish Solutions Alumina Ferrous based Carbides Cu, Ni alloys Pb, Sn, solder Collodial Silica Ceramics Cast irons Light metals (Al, Mg, Be) Refractory metals Polymers Printed Circuit boards

Grinding / Polishing Surface Selection Grinding SiC papers, Diamond disk, BuehlerHercules Polishing Cloths: woven/pressed, napped Woven / Pressed Napped

Grinding / Polishing Selection Theory Fixed abrasive: The action of a given abrasive size will vary based on the bonding method and abrasive type Applied abrasive: The action of a given size abrasive will vary according to the surface on which it is charged A harder surface will cause an abrasive to act more aggressively than a soft surface The texture of the surface will also affect edge rounding and relief (this applies mostly to napped cloths)

Grinding / Polishing Surface Comparison 30 Material Removal (um/min) 25 20 15 10 5 0 Microcloth Texmet 1000 UltraPol Hercules S Hercules H Parameters: Al specimens, 9µm diamond, 150 RPM, 5 lbs/specimen

Grinding / Polishing Typical Polishing Surfaces ULTRA-PAD ULTRA-POL TEXMET 1000 TRIDENT

Typical Final Polishing Surfaces Grinding / Polishing MICROCLOTH CHEMOMET