Introduction.

To sustain Moore's law, that predicts doubling computer processing power every 18 months, new breakthroughs in core technology procedures in lithography have to be done. Particularly important is increase a resolution of lithography on surface of forming  chip as well to be able to perform precise manipulations like etching out or local increasing temperature for creating doped semiconductor zones by thermodiffusion.

There is natural limitation on the type of beam source to be able concentrate energy on the local shaped region. A wave length of illuminated particles have to be not too much larger of the minimum size of elements of chip to avoid defocusing effect of diffraction.  The logical continuations of the presently exploited technologies is to move deeper and deeper into ultraviolet area of light spectra utilizing good developed methods of optical lithography.

Other prospective option is is to switch to electron sources as a tool for formation nanoscale structures. The wave length of electrons is depend on their energy and as so can be easy controlled. The electron optics is also well explored area easy to be applied into new area of technology.

The problem to overcame in adapting a paradigm of broad usage of electron sources in semiconductor technology in general could be characterized with one word - productivity. The source of the electrons has to be bright enough to deliver reasonable yield of energy in direct impinge on material. Obviously power, programmable scanning electron microscope can perform all necessary activity but at very, very unpractical slow pace.

Prospect solution was offered by Dr. H.F. Lockwood (Emission Systems LLC) and W.B. Feller, L.P. White, P.B. White  (Nova Scientific, Inc.) presented at ML2 Workshop, 28 August 2001. The idea is to use an array of parallel sources of electron guns densely maintained at the thin disc in such way that each individual e-bean gun could be separately focused and switch on/off at will as well be able individually scanned along target to perform lithography procedures.

The heart of the idea is a micro electron amplifier. Essentially it is micro channels through a thin disc. When constant electrical voltage is applied along the channel entry electrons are accelerated inside and hit inner surface of the channel ousting secondary electrons. These secondary emitted electrons from their parts produce next generation of secondary electrons and all construction is acted as am electron beam amplifier. There is a problem: emitted electrons are leaving positive charges at the inner surface of the channel. So material of the disc has to have a contradictory property. It has to be conductor to discharge these collateral positive charge areas. In the same time it better not to be conductor to prevent parasitic electrical current across the disk. Besides that this parasitic current is just waste of energy it will change temperature of the material that can dramatically move all characteristics of the device out of working parameters.

Following is a description of the proposed solution for this problem:

Micro channel along p-n diode.

A diode is an structure of (semi)conductors these act as insulator in specific direction of electrical field. Exact what is needed for satisfying contradiction of demands to properties of the material for e-beam amplifier - not to conduct along applied electrical field and carry out extra positive changes.

The principal scheme of the E-Beam Micro-channel Amplifier is displayed in the Figure 1.

Fig 1. Principal scheme of the E-Beam Micro-channel Amplifier

The semiconductor diode contents two parallel layers of p and n doped semiconductor materials. For example it could be silicon (Si) doped with boron (B) for formation of p-doped layer that has positive holes as electric current curriers. For forming n-doped layer with electrons as an electric current curriers silicon (Si) doped with phosphorus (P), arsenic (As), or antimony (Sb) can be used. In the FIGURE 1 thicknesses of the p and n doped layers are given not in scale only for demonstration of the physical principle of the invention.

The form of the semiconductor diode is as a rule is the plate like. The silicon wafer presents an example of raw material that can be used to build the E-Beam Micro-channel Amplifier on. The inner surface of the channel could be covered with the Emissive Layer to improve secondary electron emission. The amplification of the initial electron current depends on the voltage needed to produce secondary electrons with coefficient more then one. The choice of the material for the Emissive Layer has to be based on the criteria of minimization the critical voltage for multiplication of initial electrons. The silicon oxide (SiO2) has required characteristics. Metal electrodes are put in contact with areas around both of the channel and electrical voltage is applied to them such way that negative charged (cathode) is in contact with p-doped layer of diode.

Electrons entered into the channel from the cathode side are accelerated in electrical field and occasionally hit its inside surface (Emissive Layer). If energy of the hitting electron is large then minimal needed to produce multiplicative number of secondary electrons initial electron current is amplified. Every secondary emitted electron is accompanied with the positively charged ion in the Emissive Layer that has to be neutralized. In the p-doped layer of the diode, positive charged holes are migrated to the cathode where they are neutralized with electrons. In the n-doped part of the diode electrons are current curriers these moved to the positive charged ions and neutralized them.

Direct electrical current between electrodes are suppressed as it has to be in described position of the diode relatively applied electrical voltage when cathode is attached to the p-doped semiconductor. The diode as a whole, taking aside effects accompanied secondary emission, is acted as an insulator that significantly improve the efficiency and stability of its work as an e-beam amplifier comparable to the previously known art.

FIGURE 2 illustrates a process of forming E-Beam Micro-channel Amplifier according to the one of the particular implementation of the present invention.

Fig 2. Variant of the forming of the

In this specific example will be presented a variant clearly demonstrated a principle of the production of the E-Beam Micro-channel Amplifier.

FIGURE 2. a) presents cross section presents cross section of development step of E-Beam Micro-channel Amplifier in particular an initial detail, p-doped (with boron) silicon (Si) wafer (thin disc with thickness around part of millimeter), for producing E-Beam Micro-channel Amplifier. The material of the wafer is a semiconductor with significant concentration of holes (positive charged current curriers).

FIGURE 2. b) presents cross section of development step of E-Beam Micro-channel Amplifier in particular a formed n-doped semiconductor layer from silicon deposited on one side of the silicon wafer. Alternate variant for forming n-doped layer could be implantation or deposition of the phosphorus atoms on the surface of the silicon wafer and then forming n-doped layer with thermal diffusion.

FIGURE 2. c) presents cross section E-Beam Micro-channel Amplifier formed by physical or chemical etching throughout channel in silicon wafer. Physical etching can be performed by low wave laser, electron beam or dry etching in plasma reactor. Chemical etching can be performed by combination of forming oxide layer, depositing photoresistor layer, forming directional hole in oxide layer under removed area on photoresist and plasma etching a throughout channel in silicon wafer, removing the photoresistor and oxide layers after all. There are numerous technological methods to form needed throughout channel. Step c (forming a throughout channel) can precede step of forming n-doped layer. In this case it is important to be sure that deposited layer will not close a channel.

FIGURE 2. d) presents cross section of E-Beam Micro-channel Amplifier with deposited metal electrodes on both sides of silicon wafer. Preferably metal of electrodes will be resistive to oxidation, noble metals like platinum (Pt) or gold (Au). Preferably metal electrodes will be deposited around open sides of the channel on both sides of the silicon wafer and be enough size to form electrical field along the channel. In case there are number of channels formed on wafer, all of them could be connected. Alternatively each of the channels could be connected to electrodes independently via deposited wires deposited on the surface of wafer to be able independently control electrical voltage for every E-Beam Micro-channel Amplifier. It can permit to use array of E-Beam Micro-channel Amplifiers as an element in construction of flat electronic display with multi electron guns.

FIGURE 2. e) presents cross section of development step of E-Beam Micro-channel Amplifier formed by thermo oxidation emissive layer that provides optimal coefficient of secondary emission.

FIGURE 2. f) presents cross section of E-Beam Micro-channel Amplifier in action. Electrons emitted with outside emitter are accelerated in electrical field and multiplicative reproduce in result of secondary emission. Electron lens and scanning systems placed after E-Beam Micro-channel Amplifier focus and target electron beam to perform useful work such as maskless lithography, forming image on flat display or electron microscopy on the large objects. It is further intended that any other embodiments of the present invention that result from any changes in application or method of use or operation, method of manufacture, shape, size, or material which are not specified within the detailed written description or illustrations contained herein yet are considered apparent or obvious to one skilled in the art are within the scope of the present invention.

Provisional patent application US60/810,860 can be download here.

For business propositions contact Dr. Leonid Sakharov