Physical Analysis of Semiconductor Wafers

Reducing process induced yield loss through wafer fabrication control

Control of the process steps and wafer environment to meet the daily challenges of routine wafer compliance requires the use of many diverse characterization techniques, including electron and ion microscopy. Here you will learn about Thermo Fisher Scientific electron microscopes and their use to help you control process steps throughout semiconductor manufacturing to ensure you are reaching the highest yield possible.


The role of electron and ion microscopes for physical analysis of semiconductor wafers

Controlling process steps and analyzing physical structures of the semiconductor wafer employs various high resolution optical / electron / ion microscopes and specific spectrometers / diffractometers. Table 1 lists many of these technologies, while Table 2 illustrates their use in semiconductor fabrication.

Table 1. Example technologies for physical analysis of semiconductor wafers

Optical, electron and ion microscopes Spectrometers and diffractometers
Optical Microscopy (OM) Auger Electron Emission Spectroscopy (AES)
Scanning Electron Microscopy (SEM) Secondary Ion Mass Spectroscopy (SIMS)
Transmission Electron Microscopy (TEM) X-ray Photoelectron Spectroscopy (XPS)
Focused Ion Beam (FIB) X-ray Fluorescence Spectroscopy (XRF)
  X-ray Diffraction Spectroscopy (XRD)
  µ-Raman Spectroscopy

Table 2: Overview of physical and chemical device analysis in semiconductor device manufacturing

Type of device analysis Analytical technique Analytical requirements Typical performance
Device dimensions (3D) FIB-SEM Spatial resolution, contrast, no damage < 1nm @ 1 KeV
(S) TEM Spatial resolution, contrast, no damage < 0.1nm @ 80 KeV
AFM Spatial resolution, no damage  
Chemical composition
Dopant profiles
AES, XPS, ToF-SIMS Surface analysis, lateral & depth resolution, chemical sensitivity < 20nm, ~0.1% chemical sensitivity (AES)
< 100nm lateral, < 1nm depth resolution, ppm/ppt/1e15 at/cm3 chemical sensitivity, (ToF-SIMS)
SIMS, SEM-EDX, STEM-EDX, XRF Bulk analysis, lateral & depth resolution, chemical sensitivity < 2nm, ~0.01-0.1% chemical sensitivity (STEM-EDX)
Atom Probe Tomography 3D analysis, spatial resolution Single atoms detected,
< 0.1 nm spatial resolution
Chemical contamination VPD-TXRF, VPD-ICP-MS Chemical sensitivity, reproducibility < 1e10 at/cm2, ~1E7 at/cm2 detection limits
ToF - SIMS Chemical sensitivity, spatial resolution, reproducibility < 100nm lateral, < 1nm depth resolution, < 1E8 at/cm2 detection limits
Strain,
Thermomechanical properties
Micro Raman spectroscopy
PED-STEM, CBED-STEM
Nano-indentation, Porosimeter
Sensitivity, precision, spatial resolution  
Electrical fault isolation SEM-nanoprober
AFM-nanoprober
Light emission microscope (EMM)
Laser (e.g., OBIRCH)
Lock in Thermography (LIT)
Fault isolation sensitivity and spatial resolution of the fault isolation  

Today’s wafer fabrication must deal with shrinking geometries, new materials, and novel architectures, critical device structures are simply too small to see or characterize with existing tools. As the device dimensions shrink, the requirements for image resolution and detector sensitivity become more stringent too: to visualize transistor structures in a < 10nm device, microscopes are required to have a resolution in the Angstrom range and, as the detectable signals coming from the extremely small probed volumes (< 0.001 um3) are very weak, signal detectors and read-out electronics are required to be highly sensitive and noise-free.

Thermo Fisher Scientific offers a wide range of electron and ion microscopes and other analytical instruments for wafer analysis at different stages of the industry cycles, i.e., during pathfinding and process development or during yield ramp and manufacturing.

During pathfinding and process development phases, technologists and designers push the boundaries of physics while engineering new devices at the atomic level. Thermo Fisher Scientific provides the most advanced toolsets that enable this advanced R&D to continue on the 10, 7 and even the sub-7nm technology nodes.

During the yield ramp phase it is crucial to accelerate yield learning as time to market is the key to commercial success of the new generation devices. Yield analysis at many of the steps in the manufacture of a semiconductor device used to be done with optical or SEM based tool sets, but is becoming increasingly dependent on TEM microscopy results. Thermo Fisher Scientific is enabling this transition from SEM to TEM with new high productivity tool workflows that combine highest performance with lowest cost per TEM sample.

Once the new technology has been developed and systematic process defects are eliminated during the yield ramp, high volume manufacturing requires a very precise and effective control of the critical and often marginal processes to maintain yield at economically sustainable levels. Thermo Fisher Scientific develops and proposes dedicated workflow solutions which enable high performance characterization of yield excursions in shortest time and in unprecedented volumes.

In addition to these analytical solutions for wafer analysis during the manufacturing process, Thermo Fisher Scientific product lines also include products that specifically serve Electrical Debug after Electrical wafer test or after packaged device test: Electrically failing devices need to be inspected and a root cause for the electrical failure needs to be found to be able to correct imperfections in the manufacturing process or in the electrical design. Electrical Failure Analysis consists of two vital steps, the first is to detect the physical location of the electrically defective nets in the device (fault isolation) and the second is to physically inspect that physical location on any physical or chemical device anomalies (fault identification). Fault Isolation methods are based on time modulated excitation of the device and measurement of the (also time modulated) signals emitted by the device. The device excitation can be physical (laser, heat) or electrical (electrical test vectors) and the device response can be physical or electrical as well. Lock In Thermography (LIT) is the technique where the device is uniformly heated by heat pulses of a given frequency and the local temperature response of the device is measured by a sensitive IR camera. OBIRCH (Optical Beam Induced Resistance Change) is a technique where an electrically powered device is locally heated by a pulsed laser and the response to this local heating is measured as a change in the electrical resistance of the device. In Emission Microscopy (EMMI) the device is electrically stimulated with dynamic signals by which transistors switch between on and off states and emit light. The emitted light is detected with ultrasensitive cameras with picosecond resolution. Nanoprobers, finally, can be used to contact and electrically test individual transistors in a pre-determined localized region. Nanoprobers are either SEM or AFM based.

Table 3: Thermo Scientific solutions for wafer based yield loss analysis and process control

Instrument Type Target Applications Thermo Scientific Instrument Path-finding Process Dev Yield Ramp HV Manu-facturing
High-end (S)TEM Microscope Automated STEM metrology and (EDX) Analytics Metrios        
High-end STEM
HR imaging and advanced analytics
Titan Themis        
Full Wafer DUAL BEAM FIB-SEM Systems Automated wafer-based FIB-SEM
TEM lamella preparation
Exsolve
WTP FIB/SEM
       
Wafer-based FIB-SEM
Ultimate TEM lamella preparation
Helios 1200
FWDB
       
Small Chamber DUAL BEAM FIB-SEM Systems High mill rate
Sample preparation and SEM (EDX/EBSD) inspection
(3D-IC, adv. Packaging, ME MS, etc.)
Helios Dual Beam PF IB        
High resolution (3D) SEM inspection
Ultimate TEM lamella preparation
Helios G4 Nanolab FX        
High resolution (3D) SEM inspection
Fast & automated TEM lamella preparation
Helios G4 Nanolab HX        
FIB Circuit Edit Systems FIB-OM based circuit modifications OptiFIB Circuit Edit        
HR FIB based circuit modifications V400ACE Circuit Edit        
Electrical Fault Isolation Systems Light emission & laser stimulation based fault isolation Meridian tool series
(EMMI, OBIRCH, LVx)
       
Lock in Thermography based fault isolation Elite (LIT) tool        
SPM and SEM nonoprobing SEM Flex prober
Hyperion SPM prober