A number of techniques for producing TEM cross-sections of thin films have been described in recent years as the need for improved and more-thorough microstructural study of thin-film materials has grown. We have developed a method for producing such cross-sections which involves little sophisticated equipment other than an ion mill for thinning. Following the method of Bravman and Sinclair (J. Elec. Micrs. Tech 1,53–61 (1984)), the film of interest is either deposited on or epoxied to a silicon wafer and a composite of six silicon beams (=3mm × 25mm × 0.5mm) is fabricated. Slices are cut from this composite perpendicular to the film plane, and each slice is mechanically thinned by a series of simple grinding and polishing steps to ∼ 50–100μm. Dimpling is not necessary. The specimen is mounted onto a slotted TEM grid which provides a vehicle for safe handling, and the specimen is ion milled to perforation. We have found the technique to be relatively fast, reliable, and simple. Its success hinges on minimizing the amount of direct handling required when the specimen is thin and fragile. We present a detailed recipe describing its various steps and show typical results from studies of thin films for data-storage applications.

Semiconductor materials and devices are commonly investigated by transmission electron microscopy to obtain microstructural information. The results are useful only when a thinned sample is representative of the parent material. The technique of ion milling can introduce artifacts arising from beam heating during specimen preparation. A survey of specimen temperatures during argon and iodine ion milling of silicon, indium phosphide and gallium arsenide was made by encasing a thermocouple in a specimen and varying ion beam energy and beam angle of incidence. The results indicate, for example, that the typical temperature of silicon specimen preparation is less than 140°C. By decreasing the beam energy and incident angle, the milling temperature can be reduced. Design improvements on the ion mill can also sink heat away from the specimen.

The use of two methods for preparation of TEM samples has been investigated. It has been possible to show the practical details of the wedge cleaving method and illustrate it with original results on III-V semiconductors and on metallic thin layers on Silicon. Chemical etching of AlGaAs in heterostructures was clearly observed and can further be quantified. Preferred oxidation of AlAs was shown to be important this can be a problem to a faithful interpretation of images from cross section samples prepared in more conventional ways. Efficient microtomy for use in materials science is still in the development stage, however we think to have found the best conditions for sectioning very soft metals like copper. We hope to decrease the compression in these materials by using lower angle diamond knives

A procedure for preparing cross-sectional TEM specimens by focused ion beam etching (FIB) of specific regions on an integrated circuit chip is outlined. The investigation of the morphology, structure and local chemistry of precisely selected regions of semiconductor devices becomes increasingly important since the lateral dimensions and layer thickness of device structures are continually being reduced. The standard technique of preparing specimens for TEM, whether planar or cross-sectional, cannot select particular small regions. Some techniques and a number of tools and fixtures have been proposed which allow us to prepare TEM specimen of prespecified locations in complex devices. Most of these techniques, however, are still very difficult, tedious process and time consuming.

A new technique has been proposed recently involving the use of FIB. The technique ensures that the preselected area of submicron scale will be located in the electron transparent section used for TEM imaging, in preparation turn-around time of about two hours. The TEM imaging of specific contacts via hole in a VLSI chip is illustrated.

Methods were investigated for the rapid preparation of cross-sectional TEM samples from electroplated copper. Electropolishing and ultramicrotomy were used. The electropolished samples were sandwiched in a copper/nickel alloy and electropolished using a nitric acid/methanol mixture. Large transparent areas were obtained and it was possible to position the area of interest at the point where the hole would appear. Ultramicrotomed samples cut with 45° diamond knives were electron transparent but the crystalline structure of the sample was severely damaged. However, it was possible to identify the conditions by which good ultramicrotomed samples might be produced in the future.

We have developed and used a simple lithographic technique that allows preparation of TEM sections from a variety of materials in 10–45 minutes. To obtain TEM sections, 50–5,000 Å diameter cylindrical post structures are microfabricated on the surface of the sample using colloidal particles as an etch mask. The technique simultaneously prepares 104 – 108 posts. This not only allows a statistical characterization of sample structure but also provides enough material for studies of the electronic, spectroscopic and chemical properties of edge sites exposed on the post surfaces. These lithographically prepared posts have been used to study the structure of materials as diverse as a layered transition metal chalcogenide catalysts, semi-insulating polysilicon, amorphous semiconductor superlattices, crystalline metallic and semiconductor superlattices, and molecular-scale microporous superlattices.

The delineation of n-p junctions is one of the techniques routinely required in the analysis of electronic devices. The delineation of the junction profile is typically done either in a scanning electron microscope (SEM) or by angle lapping / staining/ optical microscopy. Recently TEM foils have been selectively etched to simultaneously provide an interface demarcation and an image of processed induced dislocations. A case study is presented in this report on concentration dependent delineation techniques with emphasis on the special problems associated with cross sectional transmission electron microscopy (XTEM) samples. The etchants used in delineating junctions for the SEM or with angle lapping / optical microscopy of transistors are too aggressive for the extremely thin TEM foils. This paper discusses etchants which deliver reproducible, high contrast delineations in XTEM samples with known concentration profiles.

We have modified a conventional dimpling machine to perform chemical polishing with a reactive etchant. The modified dimpler also detects specimen perforation in situ optically, and automatically stops the dimpling process by lifting the dimpler wheel and flooding the specimen with a rinse solution. Using this apparatus, we are able to prepare both planar and cross-sectional thin specimens of compound semiconductor materials without using expensive and time-consuming ion-milling. The specimens have large thin areas, are free of artifacts, and are suitable for high-resolution lattice imaging.

Thin polysilicon layers are used in microelectronics as a first metal level. With careful annealing, a doped polysilicon layer can also act as a diffusion source for the underlying Si substrate. For such a case, the quality of the polysilicon to substrate Si interface plays an important role in the electrical and migratory properties of the final structure. Therefore, the interface must be observed very closely.

Arsenic doped polysilicon was deposited on a <001> oriented Si wafer. Cross-section TEM specimen preparation was performed by first cutting dices centered on the prespecified region of interest. The dices are bounded face to face, and then a parallel double face mechanical polishing of the section reduces the thickness of the cross-section to about 30 microns. An ion milling operation is used to finish the preparation. Localisation precision by this method is not better than 100 microns, but this can be improved to 10 microns by replacing one of the dices with a piece of glass to allow visualization of the surface during polishing.

The advantage of this method is that a large region can be observed, 1.5 mm long on each piece, with rather good localisation.

An application is the HREM imaging of a typical interfacial region. We could see an ultrathin (1nm) amorphous layer running along the interface between the Si and the polysilicon. Physical characterization (EDXS, EELS) was obtainable from this ultrathin layer.

Modifications to conventional techniques required to prepare specimens from magnetic recording disks are described. Both the preparation of through-foil and cross-section specimens are discussed. The differences between preparation techniques for particulate and thin film disks are elucidated. Micrographs of specimens prepared by various techniques from both types of disk technology are presented that show the relative merits of these methods.