Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-01-22
2001-01-30
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06180291
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to an apparatus used in the fabrication of semiconductor devices, and more specifically, to a reticle used in the manufacture of semiconductor devices employing photolithography.
2. Description of Related Art
The use of lithographic technology in transferring patterns from photomasks to semiconductor substrates in the fabrication of semiconductor devices, such as integrated circuits, has been highly developed and widely used. Reticles, or photomasks, are used with a variety of radiation sources, both visible and ultraviolet, as well as x-rays and electron beams.
A typical reticle comprises a transparent substrate, such as glass, quartz and the like, which is coated with a masking layer patterned to be complementary to the pattern desired to be transferred to a silicon wafer. Such masking layers are generally materials such as chromium, chrome oxide, iron oxide, nickel and the like. These materials are deposited on the substrate by conventional techniques known in the art.
In photolithography, transmission of light through the substrate of the reticle is about 96.0%. Thus, about 4% of the light is reflected at the interface of the substrate facing the silicon wafer and the air. Light passing through the substrate and hitting the masking layer is completely reflected at the substrate/mask interface. The 4% inherent reflectance of the reticle at the substrate/air interface increases the exposure time to pattern the silicon wafer leading to slower production and increased cost per wafer.
The glass substrate will typically become statically charged during handling. Even the smallest amount of static charge will attract dust and particles to the glass surface further degrading the circuit pattern projected on to the semiconductor substrate.
Static electricity due to the motion of objects or air around the reticles builds up on the reticles. Electrostatic discharge (ESD) results when the opposite charge between objects reaches a threshold, and the charge is passed between the objects. Depending on the degree of charge and an object's material sensitivity, the exchange of charge can cause damage to the object. In the case of very small mask photolithographic design structures, such as reticles, this damage can be severe enough to melt and/or blast the chrome structure. This causes mask damage including opens, re-deposited chrome, and severed geometries. The damage results in wafer scrap, rework, mask repair and rebuild, and considerable engineering and manufacturing time spent on in-line inspections and defect analysis.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a reticle having reduced inherent reflectance improving the transmission of light when transferring the pattern onto a semiconductor substrate.
It is another object of the present invention to provide a reticle having optimal transmission and reduced ESD.
A further object of the invention is to provide a method of fabricating a static resistant reticle having optimal transmission and reduced ESD.
It is yet another object of the present invention to provide a method of patterning a silicon wafer in a semiconductor device with enhanced transmission of light and reduced ESD providing enhanced clarity of the reticle pattern.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a static resistant reticle using a patterning layer having optimal transmission for use in integrated circuit lithographic processes. The reticle comprises a transparent substrate, a layer of material having a first refractive index disposed over the substrate; and a layer of material having a second refractive index disposed over the layer of material having a first refractive index, wherein the first refractive index is greater than the second refractive index.
The reticle further includes a patterning layer employing a light blocking material having a desired pattern for the reticle. The patterning layer material can be selected from the group consisting of chromium, chrome oxide, copper, steel, and epoxy.
Positioning of the patterning layer may be either between the substrate and the layer of material having a first refractive index or between the layer of material having a first refractive index and the layer of material having a second refractive index wherein the layer of material having a first refractive index is disposed on the substrate. The latter positioning of the patterning layer may allow the layer of material having a first refractive index to be imbedded into the surface of the substrate wherein the upper surface of the layer of material having a first refractive index is co-planar with an upper surface of the substrate. Also, the layer of material having a first refractive index may act as an etch stop for the patterning layer in this latter position of the patterning layer.
In order to reduce the ESD damage and static charge, either one of the layers of material having a refractive index must be conductive. To further reduce ESD damage and static charge a grounding strap may extend from the conductive layer. Conductivity of at least one of the layers is adapted to reduce reticle charging during lithography. Preferably, either one or both of the layers may comprise cermet material.
The layer of material having a first refractive index is selected from the group consisting of ruthenium oxide, ruthenium oxide with alumina, indium tin oxide, indium tin oxide with alumina, and nitrogen doped ruthenium oxide. Most preferably, the layer of material having a first refractive index is ruthenium oxide. The layer of material having a second refractive index is silica.
The layer of material having a first refractive index and the layer of material having a second refractive index is adapted to be an anti-reflective coating on the reticle of the present invention wherein transmission of light is enhanced during lithographic processes. The transmission of light through the reticle is, preferably, in the range of about 98.0% to about 99.5%.
In another aspect, the present invention relates to a reticle for use in lithographic processes comprising a transparent substrate, a patterned masking layer disposed on the substrate, a layer of material having a first refractive index disposed on the masking layer, and a layer of material having a second refractive index disposed on the layer of material having a first refractive index wherein at least one of the layers is conductive to reduce ESD, and the layers together comprise an anti-reflective coating on the reticle to enhance transmission of light.
In yet another aspect, the present invention relates to a reticle for use in lithographic processes comprising a transparent substrate, a layer of material having a first refractive index disposed on the substrate, a patterned masking layer disposed on the layer of material having a first refractive index, and a layer of material having a second refractive index disposed on the masking layer wherein at least one of the layers is conductive to reduce ESD, and the layers together comprise an anti-reflective coating on the reticle enhancing transmission of light.
In both preferred embodiments of a reticle for use in lithographic processes, the layer of material having a first refractive index comprises, preferably, cermet material, most preferably, ruthenium oxide having a thickness of about 50 Å to about 1000 Å. Even more preferably, the ruthenium oxide further includes a layer of alumina having a thickness of about 100 Å to about 1000 Å. Preferably, the layer of material having a second refractive index comprises cermet material, most preferably silicon dioxide having a thickness of about 100 &angs
Bessy Andrew
Doyle James P.
Gross Vaughn P.
Guarnieri C. Richard
Heh Rick J.
DeLio & Peterson LLC
International Business Machines - Corporation
Peterson Peter W.
Rosasco S.
Walter, Jr. Howard J.
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