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Silicon Wafer-Scale Micro-Fabrication Factory Using Scanning Probe Micro-Robots

Massood Tabib-Azar* and Morton Litt**

Department of Electrical Engineering and Applied Physics
**Department of Macromolecular Science
Case Western Reserve University
Cleveland, Ohio 44106
This is an abstract for a poster to be presented at the Fifth Foresight Conference on Molecular Nanotechnology. There will be a link from here to the full article when it is available on the web.

Information processing and material technologies play a crucial role in nanofabrication and molecular assembly technologies. The tendencies of atoms to stick together in a certain way to form solids, is directly dictated by their electronic orbitals and interaction between electrons in these orbitals. Calling this "tendency" the information content of the atoms, nanotechnology can either go along with this content or it can attempt to manipulate it. The manipulation against the natural tendency of the atoms can only be done under non-equilibrium conditions. The other issue is the manipulation process itself and methods that can be used to achieve the desired structure. A very appealing scheme is to design a molecular blueprint by which the assembly can be affected. This requires a building block composed of many atoms with an overall different information content. Direct manipulation at the atomic level requires local probes or nearly autonomous micro-robots with built-in programming to build structures. All the materials and structures that can be built this way can be called "hierarchical structures and materials" because in hierarchical structures the overall structure is optimized for a given functionality while each sub-unit or sub-assembly may not be individually optimal and there is a mechanical hierarchy with identifiable layering.

Taking the route of direct manipulation, we propose a microelectronics "factory" that is entirely contained on a 400 cm2 area. Equipped with micro-reaction chambers with dedicated environmental controls and scanning probes for local deposition, the proposed "Micro-Factory" is capable of fabricating a few million devices simultaneously without any need for masks or lithography. Using an electric field, the scanning microprobes deposit materials from gas phase using a process that is very similar to the chemical vapor deposition. Due to the confinement of electric fields at the tip of the probes to a few tens of angstroms, devices as small as 10 Å x 10 Å can be fabricated. Using gas-phase metal-organic precursors, semiconductors such as Si, GaAs, GaN, and SiC, metals such as Al, Cu, Mo, W, and Pt, and oxides such as SiO2, and Al2O3, and other insulators such as Si3N4 can be deposited. These precursor gases are carried over the local tip area where relatively large electric fields (106 V/cm: field emission mode) are generated by applying a few volts to the probe. In the tip region, the electric field decomposes the precursor molecules and deposits the desired material over the substrate. By choosing the tip to substrate polarity appropriately, deposition over the tip is avoided. The rest of the decomposed precursor molecule remains in the gas phase and is carried away by the carrier neutral gas. A novel approach, that involves laterally vibrating the local probe, is used to achieve line-widths in the wide range of 10 Å to 10 µm. Local probes, depositing in parallel, efficiently cover large areas needed in integrated circuits. The speed of deposition by our proposed local probes is only limited by the rate of the material delivery by the carrier gas. In this novel approach, the deposition chamber encloses a volume that is slightly larger than the local tip-substrate volume. Thus, the whole fabrication facility is fabricated on silicon using bulk and surface micromachining used in micro-electro-mechanical systems (MEMS) technologies. All the valves, flow meters, pressure gauges and analysis tools are also fabricated using MEMS technologies and constitute an integral part of the micro-fabrication facility.

The proposed "Micro-Fabrication" facility bridges the gap between micro-technologies and nano-technologies. We will discuss the above issues and the role of interfaces and present preliminary calculations regarding the feasibility of our proposed wafer scale "Micro-Fabrication" facility.

Figure 1 shows the bottom view of a wafer-scale deposition facility. Scanning probes are enclosed in a micro-chambers with their own supply lines as shown in Figure 2. Micro-pumps and valves are all fabricated on silicon using MEMS technology already demonstrated during the past 5-10 years. Parallel local probes deposit patches of semiconductors, metals, and insulators over the substrate. These probes, combined with the linear motion of the substrate underneath them have four degrees of freedom.

Figure 1: Different micro-chambers enclosing groups of local probes can be used to deposit different materials in parallel.

[2] Figure 2: Overall view of the fabrication facility.

*Corresponding Address:
Massood Tabib-Azar, Associate Professor, Case Western Reserve University, Cleveland, Ohio 44106, ph: 216-368-6431, fax: 216-368-6039, email:
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