The physics and technology of a relatively new, short‐time, thermal processing technique, namely rapid isothermal processing (RIP), based on incoherent sources of light for the fabrication of semiconductor devices and circuits, are reviewed in this paper. Low‐cost, minimum overall thermal budget, low‐power consumption, and high throughput are some of the attractive features of RIP. The discussion of RIP, in the context of other thermal processes, history, operating principles, different types of RIP systems, various applications of RIP using single processing steps, and novel applications of RIP, including in situ processing and multistep processing, is described in detail. Current trends are in the direction of RIP‐dominated silicon integrated circuit fabrication technology that can lead to the development of the most advanced three‐dimensional integrated circuits suitable for applications such as parallel processing and radiation hardening. RIP is not only a superior alternative to furnace processing, but it is also the only way to perform certain crucial steps in the processing of compound semiconductor devices such as high‐mobility transistors, resonant tunneling devices, and high‐efficiency solar cells. Development of more accurate temperature measurement techniques and theoretical studies of heat transfer and other fundamental processes are needed. Dedicated equipment designed for a specific task coupled with in situ processing capabilities will dominate the future direction of RIP.

Rapid isothermal processing

Silicides have been a topic of intensive research for more than a decade. The driving force for these investigations has certainly been the interesting materials aspects of the silicides and their applications in integrated circuits. The advantages of easy formability and low resistivity for both CoSi2 and TiSi2 have led to an intensive use of these silicides in self-aligned processes for simultaneous silicidation of source, drain and gate. The fundamental investigations of these silicides include thermodynamic and kinetic aspects of phase formation, interactions with doped Si and related defect generation, and the interaction with oxide and metals. Specific issues related to the technological implementation of silicides in a full process will be discussed in view of the trend to scale the silicided area both in the vertical and in the lateral dimensions.

Silicides for integrated circuits: TiSi2 CoSi2

Thin Ti films sputter deposited onto single‐crystal Si, thermal SiO2, and low‐pressure chemical vapor deposited Si3N4 and SiOxNy (x≊y≊1) substrates have been rapid thermal annealed in N2 or Ar, with and without an amorphous Si overlayer, and the reactions followed using Auger elecron spectroscopy, transmission electron microscopy, electron diffraction, and sheet resistance measurements. A multilayer film is created in practically every case with each layer containing essentially a single reaction product, viz.,TiSix, TiOx, δ‐TiN, or TiNxO1−x. The results are discussed in light of published Ti‐Si‐O and Ti‐Si‐N phase diagrams.

Interactions of thin Ti films with Si, SiO2, Si3N4, and SiOxNy under rapid thermal annealing

We used depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to measure the effects of near-surface plasma processing and neutron irradiation on native point defects in β-Ga2O3. The near-surface sensitivity and depth resolution of these optical techniques enabled us to identify spectral changes associated with removing or creating these defects, leading to identification of one oxygen vacancy-related and two gallium vacancy-related energy levels in the β-Ga2O3 bandgap. The combined near-surface detection and processing of Ga2O3 suggests an avenue for identifying the physical nature and reducing the density of native point defects in this and other semiconductors.

Optical signatures of deep level defects in Ga2O3

Low energy electron-excited nano-luminescence (LEEN) spectroscopy provides electronic band gap, confined state, and deep level trap information from semiconductor surfaces and interfaces on a nanometer scale. Correlation of luminescence features with their spatial location inside a growth structure—either depth wise or laterally—also provides information on the physical origin and growth dependence of the electronically active defects that form. LEEN spectroscopy of localized states illustrates this approach for a representative set of III–V nitride interfaces, including metal-GaN Schottky barriers, GaN/InGaN quantum wells, GaN ultrathin films, AlGaN/GaN pseudomorphic heterostructures across a single growth wafer, and GaN/Al2O3 interfaces. In each case, electronic properties are sensitive to the chemical composition, bonding, and atomic structures near interfaces and in turn to the specifics of the growth process.

Nanoscale luminescence spectroscopy of defects at buried interfaces and ultrathin films

Auger electron spectroscopy measurements coupled with sputter depth profiling demonstrate that titanium silicide forms between Ti and SiO2 at conventional annealing temperatures in UHV and that rapid thermal annealing at relatively low temperatures can enhance silicide formation at Ti–Si relative to Ti–SiO2 interfaces within the same thin film structure. Reactions and diffusion at these interfaces occur on a short time scale (seconds) at low temperatures (400–700 °C), yet resemble interactions obtained at multimicron thicknesses. UHV fabrication and analysis reveals that these reactions are sensitive to interface contamination and sputter‐induced disorder.

Titanium–silicon and silicon dioxide reactions controlled by low temperature rapid thermal annealing

Low‐energy cathodoluminescence spectroscopy (CLS) is a powerful new technique for characterizing the electronic structure of semiconductor surfaces and ‘‘buried’’ metal–semiconductor interfaces. This extension of a more conventional electron microscopy technique provides information on localized states, deep‐level defects, and band structure of new compounds at interfaces below the free solid surface. Specifically, CLS provides direct identification of metal‐induced interface states which evolve in energy and density with multilayer metal coverages of the particular metal, extrinsic surface states due to lattice disruption, as well as bulk defect levels—all of which can play a role in Schottky barrier formation. From the energy dependence of spectral features, one can distinguish interface versus bulk state emission and assess the relative spatial distribution of states below the free surface. From the dependence of spectral intensity on injection level, one can spatially resolve large differences in reco...

Cathodoluminescence spectroscopy of metal-semiconductor interface structures

We have extended cathodoluminescence spectroscopy (CLS) to the study of new compound and defect formation at metal–semiconductor interfaces. CLS provides evidence for Cu2S and/or impurity band formation after laser annealing Cu on UHV‐cleaved CdS. Al deposition on UHV‐cleaved CdS followed by laser annealing leads to formation of at least two deep levels distributed at different depths from the initial interface. The energies, densities, and spatial distribution of these levels depend sensitively on the laser intensity and the presence or absence of particular metal overlayers. These results demonstrate the utility of CLS in revealing electronic features of the buried metal–semiconductor interface while still maintaining depth resolution on the order of hundreds of A or less.

Cathodoluminescence spectroscopy studies of laser-annealed metal-semiconductor interfaces

Auger electron spectroscopy/depth profiling measurements demonstrate that titanium silicide forms between titanium and silicon dioxide at conventional annealing temperatures Low‐temperature rapid thermal annealing provides a process window in time and temperature to suppress this parasitic reaction relative to silicide formation at titanium‐silicon interfaces within the same thin‐film structure

Control of titanium‐silicon and silicon dioxide reactions by low‐temperature rapid thermal annealing

We have used pulsed laser annealing to produce highly localized chemical reactions at the interface between Al and various III-V semiconductors. We employed soft X-ray spectroscopy, Auger-electron spectroscopy and sputter depth profiling to characterize the interfacial chemical composition. From the variation of reaction threshold with the semiconductor substrate, we find that melting of both a thin layer of III-V compound and the metal overlayer initiates the chemical reaction.

H. W. Richter

Papers

Titanium–silicon and silicon dioxide reactions controlled by low temperature rapid thermal annealing

Cathodoluminescence spectroscopy of metal-semiconductor interface structures

Cathodoluminescence spectroscopy studies of laser-annealed metal-semiconductor interfaces

Control of titanium‐silicon and silicon dioxide reactions by low‐temperature rapid thermal annealing

Laser Induced Chemical Reactions at the Al III-V Semiconductor Interface