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Over the last few years, the Kavli Nanoscience Institute has made a concerted effort to increasing the technical capabilities within the KNI Laboratory.
The Kavli Nanoscience Institute (KNI) Laboratory spans 10,000 ft2 across two facilities, primary among them the 7,500 ft2 controlled-environment cleanroom in Caltech's Harry G. Steele Laboratory sub-basement, where the majority of lithography, deposition, etching, microscopy, and supporting instrumentation is located. The KNI Laboratory is managed by full-time technical staff and available for use by researchers at Caltech and other academic, government and industrial institutions.
Over the past few years, the KNI has actively pursued the acquisition of sophisticated research instrumentation to add to its arsenal of nanofabrication-related capabilities, as detailed below.
Please visit the KNI Lab website for a full overview of instrumentation and capabilities, or to view usage rates and membership options.
The ALD is the most recent system to be installed in the KNI Lab. It is designed to grow thin films one atomic layer at a time under very precise deposition conditions. It is configured with a 240 mm diameter resistance-heated, RF-biased aluminum electrode with temperature control to 600 °C, and substrate sizes up to 6 inches (150 mm). There is an inductively-coupled plasma (ICP) source for plasma-enhanced ALD, as well as the more traditional thermal processes, with six precursor gases to grow a variety of high-purity oxides and nitrides.
The spectroscopic ellipsometer is a tool for optical thin film analysis that enables determination of thickness, optical constants n and k (refractive index and absorption coefficient), and allows modeling of electronic characteristics such as majority carrier concentration and band-gap. The beam incidence angle ranges from 45-90°, allowing both standard ellipsometry and transmission measurements. It is equipped with a motorized sample stage that enables wafer-scale measurements. The CompleteEASE control and analysis software possesses detailed measurement and modeling capability.
The dielectric sputter system is capable of reaching UHV pressures as low as 1E-10 Torr. It is equipped with a load lock that allows for automatic sample transfer. There are eight magnetron guns, seven 2" guns, and one 3" gun. A total of two RF and three DC power supplies can be used on any of the eight guns, some with an internal switch box allowing for one power source to be sequentially routed to different guns, enabling automatic processes without manual cable swapping. One of the DC power supplies can be operated in pulsed mode. Uniformity across a 6" wafer is <5% variation for the 2" guns. Pre-mixed targets of specific alloys and compounds may be sputtered. In addition, having multiple power supplies allows for co-sputtering of up to five materials simultaneously. Reactive sputtering may be performed by introducing oxygen and/or nitrogen into the chamber during process, allowing oxides and nitrides to be formed from pure metal targets. The pulsed DC supply is ideally suited for such reactive processes where a dielectric material is synthesized. Co-sputtering multiple elements in a reactive process can produce complex ceramics. An RF power supply is also present specifically for generating a localized plasma at the substrate. This can be used as a surface cleaner, etcher, for techniques such as ion-assisted deposition, and to assist in the reactive formation of metal-nitrides. This tool is also capable of substrate heating up to 800 °C, which can be used to facilitate reactions, alloying, to control film stress, and to control crystal growth mechanisms.
Reasons to Utilize Sputtering
The chalcogenide sputter system is capable of reaching UHV pressures as low as 1E-10 Torr. It is equipped with a load-lock for fast sample transfer. There are five magnetron guns, three 2" guns and two 3" guns. A total of three RF and one DC power supplies can be used on any of the five guns, some with an internal switch box allowing for one power source to be sequentially routed to different guns, enabling automatic processes without manual cable swapping. Uniformity across a 6" wafer is <5% variation for the 2" guns and <1.5% for the 3" guns. Pre-mixed targets of specific alloys and compounds may be sputtered. In addition, having multiple power supplies allows for co-sputtering of up to four materials simultaneously. Reactive sputtering may be performed by introducing oxygen and/or nitrogen into the chamber during processing, allowing oxides and nitrides to be formed from pure metal targets. Co-sputtering multiple elements in a reactive process can produce complex ceramics. An RF power supply is also present specifically for generating a localized plasma at the substrate; this can be used as a surface cleaner & etcher, for techniques such as ion-assisted deposition, and to assist in the reactive formation of metal-nitrides. This tool is also capable of substrate heating up to 800 °C, which can be used to facilitate reactions, alloying, to control film stress, and to control crystal growth mechanisms.
The EBPG 5200 is a dedicated direct-write Electron Beam Pattern Generator that is used to pattern large areas by high-resolution electron beam lithography. This instrument has substrate holders to handle 3" wafers, piece parts from a couple of mm to 3" diameter and up to 6.35 mm thick, and 6" mask plates. This instrument can be outfitted with substrate holders to handle up to 200 mm wafers. While this instrument can be set to operate at 20, 50, or 100 keV, it is normally set for 100 keV operation (i.e. with an accelerating voltage of 100 kV, the average energy per electron is 100 keV). The EBPG 5200 was acquired to accompany the Lab's heavily subscribed EBPG 5000+, which underwent recent upgrades to achieve specifications on par with the 5200.
Scientific / Technical Applications
The ORION NanoFab is a focused ion beam (FIB) system capable of generating three different ion beams – He & Ne from the gas field ion source (GFIS) that is aligned on the main optical axis, and Ga offset by 54°, as in a more traditional "dual beam" FIB/SEM (scanning electron microscope). The He beam, which can be formed into a sub-0.5 nm probe size, is capable of high-resolution imaging, lithography and etching, with each performing in the sub-5 nm regime. The Ne beam, with a 1.9 nm probe size, can etch sub-15 nm features with order-of-magnitude higher volume-removal rates than He, and perform sub-10 nm lithography on resist. The Ga beam, with a 5 nm minimum probe size, can remove relatively large volumes of material by direct etching. In all, the three beams, each operating over large energy ranges, provide multitudes of nanofabrication opportunities in a single system.
The Nanoscribe is a high-precision microscale 3D printer that utilizes two-photon polymerization of various photoresists. The PPGT uses its own scripting environment to control a wide variety of writing parameters and to define points and paths to be written in the chosen resist. While many resists can theoretically be used, Nanoscribe has its own specially-formulated resins optimized for their two-photon lithography system. Writing at different length scales and resolutions can be optimized by choosing the appropriate resin. The software also includes slicing capability so that CAD files in STL format can be converted to a tool path much like what is found in common FDM 3D printers. Writing can be performed across areas as large as 100 mm x 100 mm, with features approximately as small as 200 nm x 500 nm, and can be viewed in real time during the writing process.
The KNI recently took over management of the Tecnai TF-30 that is housed in the W. M. Keck Laboratory sub-basement of Caltech's Materials Science department. The TF-30 is a transmission electron microscope (TEM) that can also be operated in scanning transmission electron microscopy (STEM) mode, with a voltage range of 50 to 300 kV. Operation at 300 kV makes this the KNI's highest resolution TEM (see also the 200 kV Tecnai TF-20, which has more analytical options such as EELS and EFTEM). The TF-30 is also equipped with a high-angle annular dark field (HAADF) detector for use in STEM mode, and an energy dispersive spectroscopy (EDS) detector for compositional analysis (in both TEM mode and, most often, in STEM mode). The Serial EM program allows for automated collection of images at variable tilt angles for performing tomography.