Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-06-08
2003-04-22
Whitehead, Jr., Carl (Department: 2813)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S687000
Reexamination Certificate
active
06551926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the annealing of metals, alloys, and nitrides via electron beam irradiation. More particularly, the invention relates to low temperature, wide beam electron beam annealing of layers useful in the production of microelectronic devices.
2. Description of the Related Art
In the fabrication of microelectronic devices such as semiconductor devices, it is desirable to thermally anneal the film layers which are incorporated into such devices. This annealing step insures a layer having improved electrical and mechanical properties. That is, the material has desired low internal stress and strength characteristics and these characteristics are uniform and consistent throughout the film layer by modifying the grain structure and orientation.
It is conventional to deposit layers on a semiconductor substrate, to pattern the layers and thereafter to thermally anneal the patterned layer. For some uses, metals are annealed prior to patterning. The foregoing thermal method of layer formation has a variety of disadvantages, principally because the thermal annealing process must carried out at relatively high temperatures, generally around 850° to 1100° C. Treatment at such high temperatures may have a detrimental impact on other portions of the microelectronic device. In these other annealing techniques, the heating must be done for extended periods of time, for example up to sixty minutes. This results in a reduction of device throughput during production. It is known to anneal portions of a microelectronic device using electron beam exposure. However, such uses have been for exposing a localized portion of the device rather than for a full surface treatment. It would therefore be desirable to have a method of forming patterned, annealed layers on semiconductor substrates at reduced temperatures, and at reduced manufacturing time.
It has now been found that a thin film microelectronic device which has excellent characteristics and a fine crystal grain size can be produced by a wide beam electron beam annealing with the treatment temperatures being kept low. Therefore, fine semiconductor devices can be easily produced. Accordingly, the present invention produces high-performance thin film microelectronic devices at low cost and in high yield.
SUMMARY OF THE INVENTION
The invention provides a process for annealing a thin layer which comprises:
(a) depositing a nitride, metal, or metal alloy layer onto a substrate; and
(b) overall flood exposing said entire layer to electron beam radiation under conditions sufficient to anneal the layer.
The invention also provides a microelectronic device which comprises a substrate; a silicide, nitride, metal, or metal alloy layer on the substrate, the entirety of which layer has been overall flood exposed to electron beam radiation under conditions sufficient to anneal the layer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As a first step in conducting the process according to the invention, a nitride, metal or metal alloy is deposited onto a substrate to form a pre-annealed layer. Typical substrates include those suitable to be processed into an integrated circuit or other microelectronic device. Suitable substrates for the present invention non-exclusively include semiconductor materials such as gallium arsenide (GaAs), germanium, silicon, silicon germanium, lithium niobate and compositions containing silicon such as crystalline silicon, polysilicon, amorphous silicon, epitaxial silicon, and silicon dioxide (SiO
2
) and mixtures thereof.
Deposition of the nitride, metal, or metal alloy can be accomplished using well known methods in the art. Preferred methods of applying the nitride, silicide, metal, or alloy include PVD, CVD, sputtering, and evaporation methods.
A preferred nitride is TiN. A silicide is formed by depositing a metal on silicon and annealing the combination to form a metal silicon alloy or silicide. The silicides of the present invention can be any compound of two elements, one of which is silicon and the other a metal. However, preferred silicides include TiSi, CoSi, PtSi, NiSi. Preferred metals include aluminum, aluminum alloys, copper, copper alloys, tantalum, tungsten, titanium or other metal typically employed in the formation of microelectronic devices, and alloys thereof. Any alloy can be included as part of the present invention, however, preferred alloys include Al—Cu. The thickness of the layer is preferably from about 500 Å to about 50,000 Å, and preferably from about 2000 Å to about 12000 Å and more preferably from about 3000 Å to about 5000 Å.
In the preferred embodiment, the deposited layer is unpatterned. In certain instances the material may be patterned. In such a case the deposited layer is then imagewise patterned by standard lithographic techniques. This may be done by forming a photoresist image on the deposited layer on the substrate and then removing portions of the layer by etching. In this technique, the deposited layer is coated with a photoresist composition. The photoresist layer is then imagewise exposed to actinic radiation and developed. Photoresist compositions are themselves well known in the art and are widely commercially available. Positive working photoresists include compositions or polymers that can be solubilized or degraded as a result of irradiation with an electron beam or actinic radiation. Suitable photoresist compositions may include mixtures of o-quinone diazides with an aqueous alkali soluble or swellable binder resin such as a novolak or poly(4-hydroxystyrene). Suitable photoresists are described in U.S. Pat. Nos. 4,692,398; 4,835,086; 4,863,827 and 4,892,801. Suitable photoresists may be purchased commercially as AZ-4620, from Clariant Corporation of Somerville, N.J. Other suitable photoresists include solutions of polymethylmethacrylate (PMMA), such as a liquid photoresist available as 496 k PMMA, from OLIN HUNT/OCG, West Paterson, N.J. 07424, comprising polymethylmethacrylate with molecular weight of 496,000 dissolved in chlorobenzene (9 wt %); P(MMA-MAA) (poly methyl methacrylate-methacrylic acid); PMMA/P(MMA-MAA) polymethylmethacrylate/(poly methyl methacrylate-methacrylic acid). The photoresist of the present invention may comprise any of these materials or analogous materials provided different the composition can be solubilized or degraded as a result of irradiation with an electron beam or actinic radiation.
In a preferred embodiment, the working photoresist composition preferably comprises a solution of a novolak resin, a quinone diazide photosensitizer, and a compatible solvent composition. The production of novolak resins is well known in the art and is more fully described in U.S. Pat. No. 4,692,398. Suitable quinone diazide photosensitizers include o-quinone diazides such as naphthoquinone diazide sensitizers which are conventionally used in the art in positive photoresist formulations. Useful naphthoquinone diazide sensitizers include naphthoquinone-(1,2)-diazide-5-sulfonyl chloride, and naphthoquinone-(1,2)-diazide-4-sulfonyl chloride condensed with compounds such as hydroxy benzophenones. These compounds are also more fully described in U.S. Pat. No. 4,692,398.
After deposition onto the deposited substrate, the photoresist is imagewise exposed, such as through a mask, to actinic radiation. This exposure renders the photoresist layer more soluble after exposure than prior to exposure. The amount of actinic radiation used is an amount sufficient to render the exposed portions of the photoresist layer imagewise soluble in a suitable developer. Actinic radiation such as UV (ultraviolet), laser, writing e-beam, x radiation, etc., may be employed in the present invention. Preferably, UV radiation is used in an amount and at a wavelength sufficient to render the exposed portions of the photoresist layer imagewise soluble in a suitable developer. UV exposure doses of from about 100 mJ/cm
2
to about 300 mJ/cm
2
are usually sufficient.
Suitable developers fo
Blum David S
Electron Vision Corporation
Jr. Carl Whitehead
Roberts & Mercanti LLP
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