TEM techniques for the development of ULSI technology

Abstract

In the last decade transmission electron microscopy (TEM) has become one of the most powerful tools for the structural characterization of crystalline materials. Especially in the field of microelectronics development and production, the information obtained by this analytical tool has been of vital importance for the improvement of the different processing steps. With the reduction of the dimensions of the devices TEM is the only technique that can give information with enough spatial resolution.

In this work applications of transmission electron microscopy for the study of processing steps of ULSI technology will be presented. In the first chapter special emphasize is given to the theoretical background of transmission e Some details about Secondary Ion Mass Spectrometry (SIMS) and Spreading Resistance Probe (SRP) are also given, as they will be used for cross-correlation in the following chapters.

In semiconducting research and production the processes for the fabrication of devices are restricted to a small volume of the starting material. Only the areas close to the surface, about 5 μm deep, are used for the operation of the devices. Both for plan view and cross-section TEM investigation of integrated circuits special specimen preparation techniques had to be developed. These techniques are described in full detail in chapter two.

Chapters 3 and 4 deal with the application of TEM for the characterization of two processing steps that are required for the fabrication of ULSI devices. Chapter 3 presents a structural study of the geometry and the defect generation in the substrate for one of the most important aspects of the process: the device isolation. In it modifications of the LOCOS process will be given, which try to solve the specific problems of LOCOS when applied to submicron devices.

In chapter 4 the delineation of shallow junctions is treated. The dopant profiles have to be well characterized and analytical teehniques have to be used which have a high spatial resolution and a high sensitivity for dopant concentration. Especially the determination of two-dimensional dopant profiles poses severe problems. Special TEM techniques will be presented, which allow to determine the lateral dopant spread below implantation masks. Especially promising is the applieation of in-situ electron irradiation in a high voltage transmission electron microscope (HVEM) to this topic. It will be shown that the formation of extended defects in preferential areas of the specimens, induced by the high energy electrons, is dependent on the dopant concentration. Correlation with SIMS or SRP will allow to determine this doping level in a quite accurate way.

Finally in chapter 5 the most relevant conclusions of this work will be presented. Further research on the treated topicswill be suggested.