A developed wedge fixtures assisted high precision TEM samples pre-thinning method: Towards the batch lamella preparation

Binghai Liu,Zhihong Mai,Dandan Wang,Yamin Huang,Jeffrey Lam,Lei Zhu

doi:10.1063/1.4980022

Abstract

Ion milling, wedge cutting or polishing, and focused ion beam (FIB) milling are widely-used techniques for the transmission electron microscope (TEM) sample preparation. Especially, the FIB milling provides a site-specific analysis, deposition, and ablation of materials in the micrometer and nanometer scale. However, the cost of FIB tools has been always a significant concern. Since it is inevitable to use the FIB technique, the improvement of efficiency is a key point. Traditional TEM sample preparation with FIB was routinely implemented on a single sample each time. Aiming at cost efficiency, a new pre-thinning technique for batch sample preparation was developed in this paper. The present proposal combines the sample preparation techniques with multi-samples thinning, cross-section scanning electron microscopy (SEM), wedge cutting, FIB and other sample pre-thinning techniques. The new pre-thinning technique is to prepare an edge TEM sample on a grinding and polishing fixture with a slant surface. The thickness of the wedges sample can be measured to 1∼2 μm under optical microscope. Therefore, this fixture is superior to the traditional optical method of estimating the membrane thickness. Moreover, by utilizing a multi-sample holding fixture, more samples can be pre-thinned simultaneously, which significantly improved the productivity of TEM sample preparation.

Highlights

With continuous complementary metal–oxide–semiconductor (CMOS) device dimension scaling,[1,2,3,4] delayering a die to a specific layer for physical failure analysis has become more challenging
With the advance of semiconductor technologies, the features of the device become smaller and smaller, and the transmission electron microscope (TEM) sample preparation plays a critical role in nowadays manufacturing and research environment
To prepare a TEM sample with a given location is another challenge for above mentioned techniques and methodologies, except the focused ion beam (FIB) technique

Summary

INTRODUCTION

With continuous complementary metal–oxide–semiconductor (CMOS) device dimension scaling,[1,2,3,4] delayering a die to a specific layer for physical failure analysis has become more challenging. The methods of dimpling, electro-polishing and chemical polishing, ultramicrotomy and cleaving have the difficulties in controlling and measuring the sample thickness and in guaranteeing the integrity of the interested area to be thinned. For current leading edge technology in 20 and 14 nm beyond, the FIB time to prepare a TEM sample was increased because of the challenges of preparing ultra-thin lamella and low accelerating voltage of the ion beam applied to reduce the ion beam bombardment. We used a surface slant grinding and polishing kit to produce batch pre-thinned lamella for FIB TEM sample preparation. On surface slant grinding and polishing kit, we can do accurate measurement on the thickness of the edged sample under a conventional optical microscope, instead of traditional method of the color spectrum of the Si membrane

EXPERIMENTAL

Backside slide polishing

RESULTS AND DISCUSSION

CONCLUSION