Harald F. Okorn-Schmidt

Physical and electrical characterization of Hafnium oxide and Hafnium silicate sputtered films

Hafnium oxides and hafnium silicate films were investigated as a possible replacement for the SiO2 gate dielectric. Hafnium oxide films were formed by reactive sputtering from a single Hf oxide target in a predominantly Ar atmosphere containing small additions of oxygen. Hafnium silicates were made by adding a He-diluted silane gas for Si incorporation. By changing the silane gas flow, different Si atomic concentrations were incorporated into the Hf oxide films. Depositions were performed with the substrate held at temperatures of 22 °C and 500 °C. The chemical composition of the films was determined with nuclear techniques. Optical reflectivity was used to measure the optical band gap. The film morphology was investigated by transmission electron microscopy (TEM) and the electrical properties were measured with capacitance–voltage and current–voltage measurements using aluminum gate capacitors. TEM and electrical measurement showed that a SiO2 interfacial layer of about 3 nm formed at the Si interface du...

Characterization of silicon surface preparation processes for advanced gate dielectrics

This paper gives a short overview of issues associated with the surface preparation of silicon surfaces for advanced gate dielectrics and the appearance and nature of the wafer surface after different chemical treatments. The main portion of the paper demonstrates the use of electrochemical open-circuit potential (OCP) measurements as a simple and powerful technique to investigate and characterize wet silicon surface-preparation processes. This technique provides unique information about the evolution of semiconductor surface reactions in wet- chemical environments and permits the investigation of the kinetics of oxidation and etching processes in situ and in real time. Very good agreement between results obtained by this technique and results from multiple internal reflection-Fourier transform infrared spectroscopy (MIR-FTIR), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), and contact-angle studies is presented in this paper. A model is also presented which permits the correlation of the measured open circuit potential difference to the thickness of a growing native oxide. The etching behavior of an ultrathin thermally grown silicon oxide layer in hydrofluoric acid (HF) is discussed as a new result obtained using the OCP technique.

Enhancement of Semiconductor Wafer Cleaning by Chelating Agent Addition

To realize environmental and cost benefits it is desirable to reduce the RCA cleaning sequence from its historical SCI + SC2 combination, in which the particle-removing SC1 solution deposits certain metals, necessitating the metal-removing SC2. One approach is to add a chelating agent to the SC1. Extensive testing of SCI solutions with addition of the complexing agent 1,2-cyclohexanediaminetetraacetic acid (CDTA) were performed. CDTA was shown to he more stable than other complexing agents in SC1 solutions, facilitating significant hath life extension. Further, SC1 solutions with CDTA were shown to be capable of removing large quantities of metals from contaminated wafers, comparable to SC2, and preventing deposition of metals. An exception is aluminum, which can deposit from SC1 even with large amounts of added CDTA, but which can he removed by a subsequent dilute (1000:1) H 2 O:HCl step.

A Selective Etching Process for Chemically Inert High-k Metal Oxides

Once annealed, high-k metal oxides such as HfO 2 and Al 2 O 3 can be extremely difficult to etch by wet chemical methods. Here we describe how ion bombardment at relatively low energy (a few hundred eV) can be used to make exposed regions of annealed HfO 2 films etchable in aqueous HF-based solutions. HfO 2 layers, 2–5 nm in thickness, were deposited by atomic layer chemical vapor deposition (ALCVD) on Si substrates, annealed at 700 °C, and subjected to selected-area ion bombardment supplied by an oxygen plasma in a reactive ion etching tool. Etch times (as indicated by time to “dewet“) were examined as a function of HfO 2 thickness, the power and time of oxygen plasma treatments, post-oxygen-plasma anneals, and wet etch chemistry. Strategies for etching thicker films and additional data provided by electrochemical open circuit potential (OCP) measurements will also be discussed.