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Auger chemical state analysis for leadframe issues

Posted: 19 Aug 2013 ?? ?Print Version ?Bookmark and Share

Keywords:leadframe? NSOL? Auger Electron Spectroscopy? AES? X-Ray Photoelectron?

The chemical process X1 was introduced as part of a design of experiments to enhance the adhesion between the mould and leadframe. However, wire bond non-stick on leadframe (NSOL) was encountered, and the need to study the effect of X1 on leadframe surface became apparent. This article discusses the application of Auger Electron Spectroscopy (AES) chemical state analysis on the leadframe surface. This newly developed technique is an alternative to the chemical state analysis usually carried out by X-Ray Photoelectron Spectroscopy (XPS). In general, chemical state analysis using AES would require standard spectra or reference samples compared with XPS.

Experimental method
Ag plated copper leadframe was cut into single unit prior to AES analysis. The sample was immediately transferred to the Auger chamber to ensure less environmental effect that may influence the surface analysis. Four units of lead frame samples were analysed as below:

Sample 1: With X1 process + NSOL wire area
Sample 2: With X1 process + Weak stitch pull
Sample 3: With X1 process + Good stitch pull
Sample 4: With non X1 process + Good stitch pull

Samples 1 and 2 were identified as problematic samples while Samples 3 and Sample 4 were identified as reference samples.

Secondary Electron Microscope (SEM): This technique uses a focused beam of high-energy electrons to generate a variety of signals at the surface of solid specimens. The signals derived from electron-sample interactions reveal information about the sample including external morphology (texture) and chemical composition.

Auger Electron Spectroscopy (AES): Also known as Scanning Auger Microscopy, it is a surface analytical technique that provides elemental and chemical state information of sample surfaces. The identity and quantity of elements are determined by kinetic energy and intensity of Auger peaks where Auger electron can escape from the outer 6nm of the surface at their characteristic energy. AES is a powerful tool for determining composition material on top of few layers due to it extreme surface sensitive energy and highly spatial resolution (figure 1.

Figure 1: Auger analytical volume. The Auger spatial resolution is ~ 10nm while the escape depth is ~ 6nm from the surface.

In failure analysis laboratory for the semiconductor industry, AES is one of the common tools used for surface analysis. Field Emission Auger Microprobe (JAMP-9500F) produced by JEOL using hemispherical electrostatic energy analyser (HSA) with multi-channel detector was used to develop chemical state analysis capability. This HSA offers analysis with high energy resolution, high sensitivity, demonstrating its full effectiveness in chemical state analysis [1].

The common energy resolution used for wide scan analysis is dE/E=0.5%, which uses M5 analyser mode where the step width for energy scanning is 1eV. This setup condition will result in high sensitivity (high counts) but low energy resolution. However, for chemical state analysis purposes, the split scan is used where the energy resolution is set higher, which uses M3 analyser mode (dE/E=0.1%), and the step width for energy scanning is 0.2eV. Both wide scan analysis and split scan analysis use 10kV accelerating voltage. The probe current used for wide scan is 10nA while 100nA is used for split analysis.

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