Silicon-on-insulator (SOI) wafers are precisely engineered multilayer semiconductor/dielectric structures that provide new functionality for advanced Si devices. After more than three decades of materials research and device studies, SOI wafers have entered into the mainstream of semiconductor electronics. SOI technology offers significant advantages in design, fabrication, and performance of many semiconductor circuits. It also improves prospects for extending Si devices into the nanometer region (<10 nm channel length). In this article, we discuss methods of forming SOI wafers, their physical properties, and the latest improvements in controlling the structure parameters. We also describe devices that take advantage of SOI, and consider their electrical characteristics.

Frontiers of silicon-on-insulator

When mirror-polished, flat, and clean wafers of almost any material are brought into contact at room temperature, they are locally attracted to each other by van der Waals forces and adhere or bond. This phenomenon is referred to as wafer bonding. The most prominent applications of wafer bonding are silicon-on-insulator (SOI) devices, silicon-based sensors and actuators, as well as optical devices. The basics of wafer-bonding technology are described, including microcleanroom approaches, prevention of interface bubbles, bonding of III-V compounds, low-temperature bonding, ultra-high vacuum bonding, thinning methods such as smart-cut procedures, and twist wafer bonding for compliant substrates. Wafer bonding allows a new degree of freedom in design and fabrication of material combinations that previously would have been excluded because these material combinations cannot be realized by the conventional approach of epitaxial growth.

Semiconductor wafer bonding

Silicon wafers were first implanted at room temperature by B+ with 5.0×1012 to 5.0×1015 ions/ cm2 at 180 keV, and subsequently implanted by H2+ with 5.0×1016 ions/cm2 at an energy which locates the H-peak concentration in the silicon wafers at the same position as that of the implanted boron peak. Compared to the H-only implanted samples, the temperature for a B+H coimplanted silicon layer to split from its substrate after wafer bonding during a heat treatment for a given time is reduced significantly. Further reduction of the splitting temperature is accomplished by appropriate prebonding annealing of the B+H coimplanted wafers. Combination of these two effects allows the transfer of a silicon layer from a silicon wafer onto a severely thermally mismatched substrate such as quartz at a temperature as low as 200 °C.

https://www-old.mpi-halle.mpg.de/mpi/publi/pdf/2327_98.pdf

A “smarter-cut” approach to low temperature silicon layer transfer

A photovoltaic cell device, e.g., solar cell, solar panel, and method of manufacture. The device has an optically transparent substrate comprises a first surface and a second surface. A first thickness of material (e.g., semiconductor material, single crystal material) having a first surface region and a second surface region is included. In a preferred embodiment, the surface region is overlying the first surface of the optically transparent substrate. The device has an optical coupling material provided between the first surface region of the thickness of material and the first surface of the optically transparent material.

Method and structure for fabricating solar cells using a layer transfer process

After pioneering work in the 1980s, plasma-based ion implantation (PBII) and plasma-based ion implantation and deposition (PBIID) can now be considered mature technologies for surface modification and thin film deposition. This review starts by looking at the historical development and recalling the basic ideas of PBII. Advantages and disadvantages are compared to conventional ion beam implantation and physical vapor deposition for PBII and PBIID, respectively, followed by a summary of the physics of sheath dynamics, plasma and pulse specifications, plasma diagnostics, and process modeling. The review moves on to technology considerations for plasma sources and process reactors. PBII surface modification and PBIID coatings are applied in a wide range of situations. They include the by-now traditional tribological applications of reducing wear and corrosion through the formation of hard, tough, smooth, low-friction, and chemically inert phases and coatings, e.g., for engine components. PBII has become viable for the formation of shallow junctions and other applications in microelectronics. More recently, the rapidly growing field of biomaterial synthesis makes use of PBII and PBIID to alter surfaces of or produce coatings on surgical implants and other biomedical devices. With limitations, also nonconducting materials such as plastic sheets can be treated. The major interest in PBII processing originates from its flexibility in ion energy (from a few electron volts up to about 100 keV), and the capability to efficiently treat, or deposit on, large areas, and (within limits) to process nonflat, three-dimensional workpieces, including forming and modifying metastable phases and nanostructures.

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Plasma-based ion implantation and deposition: a review of physics, technology, and applications

We have investigated the fundamental mechanism underlying the hydrogen-induced exfoliation of silicon, using a combination of spectroscopic and microscopic techniques. We have studied the evolution of the internal defect structure as a function of implanted hydrogen concentration and annealing temperature and found that the mechanism consists of a number of essential components in which hydrogen plays a key role. Specifically, we show that the chemical action of hydrogen leads to the formation of (100) and (111) internal surfaces above 400 °C via agglomeration of the initial defect structure. In addition, molecular hydrogen is evolved between 200 and 400 °C and subsequently traps in the microvoids bounded by the internal surfaces, resulting in the build-up of internal pressure. This, in turn, leads to the observed “blistering” of unconstrained silicon samples, or complete layer transfer for silicon wafers joined to a supporting (handle) wafer which acts as a mechanical “stiffener.”

On the mechanism of the hydrogen-induced exfoliation of silicon

There has been much interest in reproducing Si exfoliation by H implantation and in understanding the mechanism leading to such a remarkably uniform shearing. We have previously demonstrated that, contrary to the initial speculation, there are in fact three distinct aspects to the process: i) the generation of damage to the crystalline material by the implantation; ii) the unique surface chemistry of hydrogen and silicon that drives the thermal evolution of this damage region and; iii) the creation of internal pressure that ultimately causes exfoliation ofthe overlying Si layer. Therefore, a detailed understanding of the exfoliation mechanism involves the study of initial damage, of H-passivation of various internal structures and of the mechanical forces exerted by trapped gases as a function of hydrogen implantation dose/depth and annealing temperature. In this work, we have used different hydrogen implantation conditions (ion energies ranging from 1 eV to 1 MeV and substrate crystallographic orientations) as well as co-implantation of a variety of other elemental species, in combination with novel spectroscopic configurations, to further explore these different mechanistic aspects.

W. L. Brown

Papers

On the mechanism of the hydrogen-induced exfoliation of silicon

Mechanism of silicon exfoliation by hydrogen implantation and He, Li and Si co-implantation [SOI technology]

Mechanism of Silicon Exfoliation by Hydrogen Implantation and He, Li and Si CO-implantation