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4. The Charge-Pumping Technique

The developed physical model of hot-carrier induced degradation is based on a representation of the interface state profile of degraded devices. Therefore, a direct comparison of the simulation results with observed ones, i.e. with N_it profiles obtained experimentally is required for model verification. Moreover, it is very important to characterize the device interface as precisely as possible. The CP technique is one of the most useful technique for measuring the density of interface and oxide traps in MOS transistors. It has been proven as a reliable probe for Si/SiO₂ interface states, such as the total number of traps, the energy and spatial distributions, and the variation of these quantities as a function of hot-carrier-injection stress. Additionally, only basic equipment is required and the set up is trivial. The technique has been a subject of many theoretical and simulation studies. These studies have resulted in the development of numerous variations of the basic technique in order to obtain more detailed information regarding the energy and spatial distribution of interface traps generated during hot-carrier stress experiments. The charge pumping method was originally proposed by Brugler and Jespers in 1969. They reported a net DC substrate current when applying periodic pulses to the gate of a MOS transistor, while keeping source and drain grounded. The current was found to be proportional to the gate area and the frequency of the applied gate pulses. It was flowing in the opposite direction to the leakage current of the source and drain to substrate diodes. They showed that the current originates from a recombination of minority and majority carriers at traps at the Si/SiO₂ interface. Therefore, the method can be used to measure the interface trap density in MOSFETs for the evaluation of device degradation. The major breakthrough for the CP method was the thorough investigation and correct explanation of the method, applied directly to MOSFET structures by Groeseneken et al. in 1984 [172].

• 4.1 Basic Principles of Charge Pumping Measurements
  • 4.1.1 Local Threshold and Flatband Voltages
  • 4.2.2 Effective Channel Length
  
  
• 4.2 Interface State Density Profile of Unstressed Device
  • 4.2.1 Verification of the Interface State Density Distribution Uniformity
  • 4.2.2 Interface State Profile of an Unstressed Device
  • 4.2.3 Impact of Pre-stressed Interface State Density Profile on HCD Modeling
  
  
• 4.3 Charge-Pumping Extraction Techniques for the Hot-Carrier Induced Interface and Oxide Trap Spatial Distributions in MOSFETs
  • 4.3.1 Local Oxide Capacitance
    • 4.3.1.1 Conformal-Mapping Method
    • 4.3.1.2 Estimation of Approach Importance Area
    • 4.3.1.3 Lee's Approach for Modeling of Local Oxide Capacitance
  • 4.3.2 Comparison of Interface State Profiles Extracted with Different Capacitance Approaches
  • 4.3.3 Extraction Techniques Description
    • 4.3.3.1 Chim's Approach
    • 4.3.3.2 Mahapatra's Approach
    • 4.3.3.3 Lee's Approach
    • 4.3.3.4 Li's Approach
    • 4.3.3.5 Extraction Methods Results Comparison
  
  
• 4.4 Analysis of the Threshold Voltage Turn-Around Effect in n-MOSFETs Due to Hot-Carrier Stress
• 4.5 HCD Caused Interface State Profile - Simulations vs. Experiment

Next: 4.1 Basic Principles of Charge Pumping Measurements Up: Dissertation Ivan Starkov Previous: 3.4.2 Analysis of WCC within Simplified Transport Schemes