Thomas Trenkler

Highly conductive diamond probes for scanning spreading resistance microscopy

Scanning spreading resistance microscopy (SSRM) is a powerful method for the characterization of Si semiconductor devices based on atomic force microscopy (AFM). It requires conductive probe tips made of doped diamond. Although various solid diamond probes have been fabricated, they could not satisfy the requirements for SSRM. Therefore, we have developed a SSRM probe composed of a pyramidal diamond tip attached to a Si cantilever. This letter describes the probe fabrication process briefly and presents excellent SSRM measurements obtained on Si calibration samples. Solid diamond tips integrated in Si cantilevers were used for SSRM showing a significantly higher dynamic range than the conductive probes known to date.

Practicalities and limitations of scanning capacitance microscopy for routine integrated circuit characterization

We have imaged several n-type metal-oxide-semiconductor transistors with different source and drain architectures to assess the feasibility of extracting useful figures of merit, such as the effective channel length of a device, from the data. By varying the dc bias on the sample we observe a shift of the junction position in the image and consider how best to interpret a set of voltage dependent images produced for a single sample. Careful attention is paid to the effects of surface variation from sample preparation and tip wear during an experiment by considering the scanning capacitance microscopy signal in the substrate as a function of applied dc bias.

New aspects of nanopotentiometry for complementary metal–oxide–semiconductor transistors

Nanopotentiometry is a scanning probe microscopy (SPM) technique providing insight in the actual working behavior of semiconductor devices under operation. In nanopotentiometry, a conductive SPM tip is used as a voltage probe in order to measure the distribution of the electrical potential on the cross section of an operating device. The information thus provided is complementary to carrier profiling and is a method for the calibration of device simulations. The suitability of alternative SPM techniques for studying ultrashallow devices under operation is examined. Measurements have been carried out in deep submicron complementary metal–oxide–semiconductor devices. The impact of the changes in the doping profile on the potential distributions has been explored using simulations and experimental results. Due to further improvements in sample preparation and measurement methodology, the response of the devices to variable bias conditions could be studied in more detail. The formation of the conductive chann...

Tip-on-tip: a novel AFM tip configuration for the electrical characterization of semiconductor devices

A novel tip configuration for atomic force microscopy (AFM) called tip-on-tip is presented. In this concept a sharp, very small tip is created on top of a large truncated pyramid. The process scheme for the fabrication of tip-on-tip is presented. It is demonstrated that very sharp metal tips can be produced in this way. Advantages of tip-on-tip when applied in semiconductor device analysis are discussed. First results concerning the transfer of the developed technology to diamond are presented.

SURFACE PASSIVATION AND MICROROUGHNESS OF (100) SILICON ETCHED IN AQUEOUS HYDROGEN HALIDE (HF, HCL, HBR, HI) SOLUTIONS

The surface reactivity of hydrogen‐passivated, HF‐last‐cleaned Si(100) toward aqueous HX and HF/HX (X=Cl, Br, I) is examined. The HCl and HBr solutions are found to leave the HF‐cleaned bare Si surface unaltered, while the HI solution reoxidizes the hydrogen‐passivated surface. Treatments in aqueous HF/HCl or HF/HBr solutions lead to the same surface passivation and surface microroughness as for HF‐cleaned surfaces. In the HF/HI solution, a simultaneous oxidation and etching process takes place, resulting in an increased (111) microfaceting of the Si(100) surface.

Fabrication and use of metal tip and tip-on-tip probes for AFM-based device analysis

Different techniques based on the atomic force microscope (AFM) have been developed in the last few years for the electrical characterization of semiconductor devices. The quality of these measurements strongly depends on the tip which should not only have a small radius of curvature but also a high electrical conductivity. Therefore, the choice of metal as tip material is obvious. We have developed a process scheme for the fabrication of pyramidal metal tips which are integrated into a silicon cantilever. This paper discusses this process in detail and shows how the transition was made from prototyping to batch friction using standard 150 mm silicon wafer technology. Results are presented concerning the application of such probes for two-dimensional carrier profiling of InP and silicon structures using scanning spreading resistance microscopy (SSRM) and scanning capacitance microscopy (SCM). A novel tip configuration called tip-on-tip has also been developed. This concept looks promising for future applications. We demonstrate how such a tip-on-tip configuration can be realized.

Two-dimensional profiling in silicon using conventional and electrochemical selective etching

One of the methods to delineate a two-dimensional dopant profile in Si devices is the selective etching technique combined with imaging of the doping dependent topography by atomic force microscopy. A major problem of the etching procedures reported so far is the critical control of the etch duration of only a few seconds as well as a limited sensitivity and dynamic range. We report further improvements of the conventional technique and compare it to an alternative approach. Etching experiments were carried out in an electrolytic cell, whereby the etching is controlled potentiostatically. Better control of the dissolved volume is achieved through current integration. Buffered HF as the electrolyte replaces the difficult nitrogen related chemistry of the classical approach. The etch rates thereby decrease by a factor of 10–100 thus allowing for a longer etch duration. The basic mechanisms, the sensitivity, and the dynamic range of the two techniques have been studied by using homogeneous samples and specia...

Towards routine, quantitative two-dimensional carrier profiling with scanning spreading resistance microscopy

Recent developments in scanning spreading resistance microscopy have enabled to move the technique from the laboratory phase to a commercially available method for 2D-carrier profiling. In view of the large tip consumption methods and software have been developed to arrive at a rapid collection of calibration curves and the characterization of tips. These calibration curves have been integrated in a software package for quantification such that 2D-images can be completely quantified. Scanning Spreading Resistance Spectroscopy (SSRS) has been developed whereby full I-V curves can be collected at every pixel. These developments contribute to a better understanding of the physics of the point-contact, allow to characterize in more detail the electrical behavior of various tips and provide a unique signature for junction identification.