Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-11-08
2004-03-30
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S030000
Reexamination Certificate
active
06713389
ABSTRACT:
The present invention relates to a method of forming two- or three-dimensional structures using drop on demand printing. In preferred embodiments, the invention relates to
the formation of an electronic device;
the formation of an electrical circuit element;
the formation of a sensing device; and
the formation of at least part of a monochrome or colour display on a surface.
Electronic devices, and in particular integrated circuits, are the basic elements of electronic circuits. Integrated circuits typically consist of a number of discrete layers, formed from insulating, semiconductor or electrically conducting material, formed on a substrate, for example, a semiconductor substrate. These layers can form part of a component of the integrated circuit, such as a transistor, an interconnection between components, or provide an isolation barrier between components.
Conventional techniques for the fabrication of devices involve a number of different processes for forming the various layers which make up the device. Such processes include:
photolithography;
vacuum deposition;
chemical vapour deposition;
oxidation;
etching;
masking; and
dopant diffusion.
The number of processes required to manufacture, for example, a field effect transistor makes the manufacturing process slow. In addition, the use of processes such as etching and dopant diffusion which are difficult to accurately control can lead to loss in accuracy in the shape and performance of the finished product.
Drop-on-demand printing is a known printing technique whereby a droplet of ink is ejected from a inkjet printhead. The droplet impacts with a porous or semi-porous surface, dries and forms a spot which forms a recognisable pattern and colour such as type.
According to one aspect of the present invention there is provided a method of forming an electronic device using the technique of drop on demand printing to deposit droplets of deposition material, said method comprising depositing a plurality of droplets on a surface to form a patterned electronic device comprising multiple discrete portions.
The term “drop on demand” printing includes, but is not limited to, the use of a digitally defined pressure pulse (thermally, piezoelectrically, magnetically, biological or otherwise generated) that forces the fluid meniscus out of the nozzle and into contact with a substrate surface before constriction occurs, in which the fluid is transferred from the droplet deposition apparatus to the surface due to the difference between intrinsic fluid bond strength and surface adhesion/tension effects.
The present invention can make use of an ink-jet printhead to eject droplets of one or more custom fluids that coalesce on a surface and when suitably dried form a three-dimensional feature comprising at least one, preferably most, or more preferably all of the elements necessary to form an electronic device.
The key to being able to partially or completely print, for example, a polymer field effect transistor resides in an in-depth understanding of the nature of polymeric interfaces and surfaces (polymer-polymer, polymer-dielectric, and polymer-metal) that make-up the device structure. This is especially so given the dynamic nature of the ink jet print and contact transfer processes. The subject of organic device manufacture coupled with ink jet printing is a rich avenue for both scientific and technological research and development not just covering the areas cited in this patent application but also covering hitherto unexplored ideas that will be fuelled by the high degree of processing flexibility that is provided by ink jet printing in electronic, opto-electronic, and optical device manufacture. The contact type and density (contact intimacy and barrier formation mechanism and height and nature of the structure) has a profound influence on the device performance. Given that the interfaces, and hence the surfaces prior to forming an interface, are of key importance it will come of no surprise to learn that the cleanliness state of such surfaces may be crucial. Moreover, the associated surface electronic state and surface energy plays a significant role in the behaviour of the liquid droplet or transferred fluid on the surface that results initially in a liquid-solid interface that converts to a solid-solid interface after the printed liquid undergoes solidification. Of particular importance is the differential energy resulting from the interaction of the liquid (surface tension energy) with the solid surface (surface energy) to be printed on. The dynamics of the liquid on the surface, coupled with the solid concentration and solvent(s) type (mix ratio for two or more solvents) has a profound influence of the morphology of the printed solid. Whether printing on to a polymer surface or printing a polymer on to a surface there are some fundamental properties of “ideal” polymer surfaces that should be noted:
(i) the polymer surface may vary from partially polycrystalline to amorphous. With the exception of the polydiacetylenes, single crystal polymer surfaces are essentially unknown.
(ii) light emitting polymers tend to large, reasonably flexible, covalently bonded chains. The polymer surfaces generally consist of gently curved sections of the polymer chains, with occasional chain ends also being present. The polymer chains can be preferentially parallel or perpendicular to the surface. Of particular importance is the fact that surface energy effects can drive some side groups to be oriented preferably “out” from the surface or “in” towards the bulk of the film formed from the printed liquid, forming a variety of conformations.
(iii) the electronic surface region has dimension in the range of about 0.1 nm (1 angstrom) to 1 nm (10 Angstroms), although mechanical and chemical properties of the surface may influence the bulk material performance to a greater depth.
(iv) inorganic crystalline lattice (3-D periodicity) surface state formation defects are rarely observed on carefully prepared polymer surfaces. Dangling and unsatisfied surface bonds are rarely observed. For conjugated polymers the covalent bonds are satisfied and the largely one-dimensional nature of the polymer chains is preserved despite the gentle curvature, bending and end chain termination occurring at or near the surface.
The device structure is preferably so designed as to facilitate good interfacial reaction between the printed layers that make-up the device. The use of vertical walled structures with incorrectly defined surface wetting can lead to ineffective electrical contact at the interface thereby providing a device that will at best work outside the specified range or at worst will fail in service.
Suitable liquids that can be ink jet printed or contact transferred to provide conductive, semiconductive, insulating, and opto-electronic function include, but are not limited to, inorganics, organics, hybridised inorganic-organic systems, and polymer-based materials compatible with conventional evaporation or radiation enhanced drying, low temperature crystallisation, annealing, or curing, and radiation cross-linking or chemical bond scission or reformation.
In one preferred embodiment, the electronic device is a transistor, such as a field effect transistor, preferably for a multiple layer printed structure. The transistor may be an “all-polymer” transistor, each component of the transistor being formed from polymeric material. The printing technique can be applied to single or multiple layers of the device, for example, the organic semiconductor and/or insulator, and can also be applied to the complete printing of the device, including semiconductor layer, insulating layer, metallic contacts and the encapsulation and protective coating layers.
In order to fabricate a polymer transistor, drop on demand printing may be employed for one or more of a number of key layers, such as:
(i) Gate Dielectric
The key materials of interest for the gate dielectric include, but not limited to, BenzoCycloButane (BCB), polysiloxane, polyaniline, and polymethyl methacrylate (PMMA).
(i
Nelms David
Vu David
Wolf Greenfield & Sacks P.C.
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