Diffusion in silicon of elements from columns III and V of the Periodic Table is reviewed in theory and experiment. The emphasis is on the interactions of these substitutional dopants with point defects (vacancies and interstitials) as part of their diffusion mechanisms. The goal of this paper is to unify available experimental observations within the framework of a set of physical models that can be utilized in computer simulations to predict diffusion processes in silicon. The authors assess the present state of experimental data for basic parameters such as point-defect diffusivities and equilibrium concentrations and address a number of questions regarding the mechanisms of dopant diffusion. They offer illustrative examples of ways that diffusion may be modeled in one and two dimensions by solving continuity equations for point defects and dopants. Outstanding questions and inadequacies in existing formulations are identified by comparing computer simulations with experimental results. A summary of the progress made in this field in recent years and of directions future research may take is presented.

Point defects and dopant diffusion in silicon

The etch rates for 317 combinations of 16 materials (single-crystal silicon, doped, and undoped polysilicon, several types of silicon dioxide, stoichiometric and silicon-rich silicon nitride, aluminum, tungsten, titanium, Ti/W alloy, and two brands of positive photoresist) used in the fabrication of microelectromechanical systems and integrated circuits in 28 wet, plasma, and plasmaless-gas-phase etches (several HF solutions, H/sub 3/PO/sub 4/, HNO/sub 3/+H/sub 2/O+NH/sub 4/F, KOH, Type A aluminum etchant, H/sub 2/O+H/sub 2/O/sub 2/+HF, H/sub 2/O/sub 2/, piranha, acetone, HF vapor, XeF/sub 2/, and various combinations of SF/sub 6/, CF/sub 4/, CHF/sub 3/, Cl/sub 2/, O/sub 2/, N/sub 2/, and He in plasmas) were measured and are tabulated. Etch preparation, use, and chemical reactions (from the technical literature) are given. Sample preparation and MEMS applications are described for the materials.

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Etch rates for micromachining processing

The outstanding properties of SiO2, which include high resistivity, excellent dielectric strength, a large band gap, a high melting point, and a native, low defect density interface with Si, are in large part responsible for enabling the microelectronics revolution. The Si/SiO2 interface, which forms the heart of the modern metal–oxide–semiconductor field effect transistor, the building block of the integrated circuit, is arguably the worlds most economically and technologically important materials interface. This article summarizes recent progress and current scientific understanding of ultrathin (<4 nm) SiO2 and Si–O–N (silicon oxynitride) gate dielectrics on Si based devices. We will emphasize an understanding of the limits of these gate dielectrics, i.e., how their continuously shrinking thickness, dictated by integrated circuit device scaling, results in physical and electrical property changes that impose limits on their usefulness. We observe, in conclusion, that although Si microelectronic devices...

Ultrathin (<4 nm) SiO2 and Si-O-N gate dielectric layers for silicon microelectronics: Understanding the processing, structure, and physical and electrical limits

Process gas discharged from a bypass pipe to a gas exhaust system can be prevented from diffusing back to the inside of a process chamber without having to install a dedicated vacuum pump at the downstream side of the bypass pipe. The substrate processing apparatus includes a process chamber accommodating a substrate, a gas supply system supplying process gas from a process gas source to the process chamber for processing the substrate, a gas exhaust system configured to exhaust the process chamber, two or more vacuum pumps installed in series at the gas exhaust system, and a bypass pipe connected between the gas supply system and the gas exhaust system. The most upstream one of the vacuum pumps is a mechanical booster pump, and the bypass pipe is connected between the mechanical booster pump and the rest vacuum pumps located at a downstream side of the mechanical booster pump.

Substrate Processing Apparatus

A lid assembly for a semiconductor processing system is provided. The lid assembly generally includes a lid having first and second opposed surfaces, a plurality of controllable flow channels extending from the first and second opposed surfaces and a gas control system disposed on the first surface and operably opening and closing the channels. The gas control system includes a gas manifold disposed on the lid, at least one valve coupled to the gas manifold and adapted to control a flow through one of the flow channels, a reservoir fluidly connected to the gas manifold, and a precursor source fluidly connected to the reservoir.

Lid assembly for a processing system to facilitate sequential deposition techniques

A novel cold wall single wafer rapid thermal/microwave remote plasma multiprocessing reactor comprising a vacuum chamber having means for mounting a wafer in the chamber, means for providing optical flux mounted adjacent one wall facing the back side of the wafer for optical heating of the wafer, and ports for plasma injection such that remote plasma can be generated and pumped into the chamber. Ports are provided for gas injection both through the plasma generating chamber and for non-plasma injection. The plasma and non-plasma ports are connected through separate manifolds to a plurality of gas sources. The comprehensive reactor design is such that several wafer processing steps can be done sequentially in situ, while providing for optimization of each processing step.

Thermal/microwave remote plasma multiprocessing reactor and method of use

A process utilizing a microwave discharge technique for performing direct nitridation of silicon at a relatively low growth temperature of no more than about 500° C. in a nitrogen plasma ambient without the presence of hydrogen or a fluorine-containing species. Nitrogen is introduced through a quartz tube. A silicon rod connected to a voltage source is placed in the quartz tube and functions as an anodization electrode. The silicon wafer to be treated is connected to a second voltage source and functions as the second electrode of the anodizing circuit. A small DC voltage is applied to the silicon wafer to make the plasma current at the wafer and the silicon rod equal and minimize contamination of the film.

Low-temperature direct nitridation of silicon in nitrogen plasma generated by microwave discharge

This paper presents an extensive review of our work on thermal nitridation of Si and SiO 2 . High-quality ultrathin films of silicon nitride and nitrided-oxide (nitroxide) have been thermally grown in ammonia atmosphere in a cold-wall RF-heated reactor and in a lamp-heated system. The growth kinetics and their dependence on processing time and temperature have been studied from very short to long nitridation times. The kinetics of thermal nitridation of SiO 2 in ammonia ambient have also been studied. In nitroxide, nitrogen-rich layers are formed at the surface and interface at a very early stage of the nitridation. Then the nitridation reaction mainly goes on in the bulk region with the surface and near interface nitrogen content remaining fairly constant. Our results also indicate the formation of an oxygen-rich layer at the interface underneath the nitrogen-rich layer whose thickness increases slowly with nitridation time. The nitride and nitroxide films were analyzed using Auger electron spectroscopy, grazing angle Rutherford backscattering, and etch rate measurements. MIS devices were fabricated using these films as gate insulators and were electrically characterized using I - V, C - V , time-dependent breakdown, trapping, and dielectric breakdown techniques. Breakdown, conduction, and C-V measurements on metal-insulator semiconductor (MIS) structures fabricated with these films show that very thin thermal silicon nitride and nitroxide films can be used as gate dielectrics for future highly scaled-down VLSI devices. The electrical characterization results also indicate extremely low trapping in the nitride films. The reliability of ultrathin nitride was observed to be far superior to SiO 2 and nitroxide due to its much less trapping. Studies show that the interface transition from nitride to silicon is almost abrupt and the morphology and roughness of the interface are comparable to the SiO 2 -Si interfaces.

Thermal nitridation of Si and SiO 2 for VLSI

Nitroxide thin films have been grown by rapid thermal nitridation of oxidized silicon in ammonia. The kinetics of formation of the surface and interface nitrogen‐rich layers has been investigated and correlated to the electrical behavior of these films. It could be concluded that rapid thermal nitridation of ≊100 A SiO2 results in negative shift of flatband voltage, slightly increases the surface state density, increases the low‐field conductivity, reduces the high‐field conductivity, improves the dielectric breakdown field, modifies the trapping behavior of the insulator, and slows down the generation rate of new surface states due to high‐field electrical stress.

Rapid Thermal Nitridation of SiO2 for Nitroxide Thin Dielectrics

A method and apparatus for multi-zone injection apparatus of multiple process gases onto a work piece during manufacture. The multi-zone injection apparatus uses a gas injection plate with multiple injection zones to deliver the multiple process gases into the chamber for deposition onto the work piece (for example, a silicon wafer). The gas showerhead separates the multiple process in a manner that avoids premixing the process gases, thereby minimizing gas-phase nucleation and particulate generation. The showerhead also allows real-time independent control over the gas flow rates in N channels to achieve deposition uniformity. Different gases can be configured in adjacent channels to provide M zones of multi-gas radial control.

Mehrdad M. Moslehi

Papers

Thermal/microwave remote plasma multiprocessing reactor and method of use

Low-temperature direct nitridation of silicon in nitrogen plasma generated by microwave discharge

Thermal nitridation of Si and SiO 2 for VLSI

Rapid Thermal Nitridation of SiO2 for Nitroxide Thin Dielectrics

Multi-zone gas injection apparatus and method for microelectronics manufacturing equipment