Overview

The facility consists of a novel, highly instrumented CVD reactor and an attached multi-technique characterization system for the growth and real-time characterization of device-quality semiconductors. Its several integrated real-time growth characterization tools include reflection high-energy electron diffraction (RHEED) at high pressures, and Fourier transform infra-red spectroscopy/attenuated total reflectance spectroscopy (FTIR/ATR). The addition of reflection difference spectroscopy (RDS) is planned for the near future. The characterization chamber houses in-situ scanning tunneling microscopy and scanning tunneling spectroscopy (STS) instrumentation. Ex-situ characterization facilities include, atomic force microscopy (AFM) and near-field scanning optical microscopy (NSOM). The CVD reactor typically is operated at from 10^-6 to 10^-2 Torr. Rapid heating and cooling of the substrate is possible.

CVD Reactor Capabilities

The cold-walled CVD reactor maintains an ultra-high vacuum base pressure. High pumping speed at typical growth pressures from 10^-6 to 10^-2 Torr are achieved using a 600 l/s magnetic-levitating bearings turbo-molecular pump, allowing for complete gas exchange in seconds. Rapid substrate heating is provided by 6 high-voltage Krypton arc lamps mounted externally to the reactor. Rapid substrate cooling is then attainable using a "radiation quench" improving the ability to freeze in growth-front composition and morphology. The reactor accommodates full sized wafers (up to 4 in. diameter) allowing for post-growth processing for device manufacture.

High-Pressure Reflection, High-Energy Electron Diffraction and Reflection, High-Energy Electron Loss Spectroscopy

The evolution of structure and morphology during CVD can be followed dynamically with the high-pressure RHEED system. This capability offers a direct window into atomistic processes occurring during CVD. For example, changes in growth-mode (e.g., cluster formation), surface structure, and surface roughness are all reflected in the quality of the RHEED pattern. With the recent addition of a RHEELS analyzer, surface composition can be determined from core-level loss features. In addition, energy filtered RHEED, discriminating against high-energy inelastic scattering, will allow for a quantitative determination of surface roughness.

Fourier Transform Infrared/Attenuated Total Reflectance Spectroscopy

FTIR/ATR spectroscopy provides the capability to probe surface chemistry on the true monolayer scale. Bevel-cut Si wafers are used for substrates and act as waveguides for the IR radiation transmitted through the reactor using BaF viewports. Vibrational modes of atoms and molecules adsorbed on the surface are then probed. This capability has been extremely useful in determining the decomposition pathways for precursors used for CVD. The value of the probe in the study of SiGe alloys has been extended by dosing an as-grown sample with atomic hydrogen. Information on true surface composition can then be obtained by measuring the relative strengths of Si-H and Ge-H vibrational modes.

This facility is available for collaborative research projects with the investigators in IRG 1. Contact: M.G. Lagally, lagally@engr.wisc.edu.