Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2001-02-23
2002-10-01
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S311000, C430S313000, C438S724000
Reexamination Certificate
active
06458508
ABSTRACT:
This invention relates to the integrated circuit (IC) fabricating processes using photolithographically patterned photoresist materials of the type whose solubility or insolubility is acid-catalyzed during development of the photoresist. More particularly, the present invention relates to a new and improved method of protecting the acid-catalyzed photoresist material from the adverse influence of chemically-basic contaminants, such as ammonia, which are inherently generated by components of the IC as it undergoes fabrication. The present invention permits more precise and resolved etching of the components of the IC during fabrication, which leads to fewer failed ICs due to fabrication defects.
BACKGROUND OF THE INVENTION
The evolution of integrated circuits (ICs) has involved the continued miniaturization of its components. In addition to reducing the size of the individual components, the spacing or resolution between the various components of the chip has also diminished. The current resolution standard is a sub-micron spacing, in the neighborhood of 0.2 microns. It is expected that future generations of ICs will have even smaller resolutions.
The basic method for forming most of the components of an IC a photolithographic patterning process. A typical photolithographic patterning process involves placing photoresist material on the IC structure and exposing the photoresist to light using a negative or positive mask of the pattern of components. The exposed photoresist material is thereafter developed. The light-exposed photoresist material becomes soluble, which allows it to be washed away. The unexposed photoresist material is undissolved. The soluble areas are removed to provide an opening in the remaining durable mask areas. The open areas define a pattern for the components to be formed, typically by depositing, etching and implanting materials within the exposed areas while the remaining, intact areas shield the other areas. Some types of photoresist materials work in reverse, where the light-exposed areas become the durable mask-like areas and unexposed areas remain soluble and ultimately form the open areas.
In order to obtain the very small resolutions to form the components, the photolithographic patterning process must be capable of patterning and developing the photoresist material with better resolution than the spacing between the finished components of the IC. Photoresist materials which are capable of achieving such high resolutions are very sensitive to the wavelength of the exposure light. A higher degree of resolution in exposure of the photoresist materials requires a shorter wavelength of exposure light. In essence, there is a inverse relationship between the wavelength of the exposure light and the resolution of the developed photoresist materials.
The current generation of photo resist materials respond to wavelengths in the range of approximately 248 nm. It is expected that future generations of photoresist will be capable of securing even higher resolutions and will require exposure light at wavelengths of less than 200 nm. Light sources capable of generating these shorter wavelengths are laser or soft x-ray light sources. The amount of light energy from these sources is significantly low. For example, 248 nm wavelength sources generate in the neighborhood of 5-10 millijoules of energy. By way of comparison, previous types of photoresist material responded to wavelengths in the range of 436 nm, and arc lamp sources which generated those wavelengths were capable of delivering on the order of 100-250 millijoules of energy. The polymeric molecular characteristics of current photoresist materials have been adjusted to obtain good contrast despite the lower energy available from the lower wavelength light sources. Thus, even though exposed to lesser-energy light sources, modern photoresist materials must still obtain significant contrast between the exposed and the unexposed areas. Contrast is responsible for defining the edge characteristics of the features of the components formed on the chip and the resolution between those components.
To respond to shorter wavelengths of lesser power, modern photoresist materials are formed from polymeric chain molecules which contain acid moieties that catalyze to amplify the response initially established by exposure. The initial exposure to light releases some of the acid moieties from the polymeric chains. However, when the exposed photoresist material is thereafter heated, the initially released acid moieties then attack and destroy adjacent polymeric chains and catalyze the release of hundreds or thousands of other acid moieties from adjoining polymeric molecules of the photoresist material. These released acid moieties attack and effectively destroy the polymer chains of the photoresist material in a thorough and complete manner. The broken polymeric chains make the photoresist material soluble so that the open areas can be exposed. The catalyzing effect of the acid moieties accounts for the increased sensitivity and resolution available from modern photoresist material. To preserve the increased sensitivity, it is necessary to assure an effective catalytic response from the acid moieties after the initial light exposure.
It has been recognized that environmental air pollutants can adversely affect the catalytic response of the photoresist. For example, airborne ammonia and ozone are two such contaminants. Ammonia is chemically basic and therefore has the tendency to react with and neutralize the acid moieties of the photoresist material. Neutralized acid moieties can no longer catalyze to destroy the polymer chains within the photoresist material. Neutralizing the acid moieties of the photoresist material results in a diminished resolution capability of the photoresist material, because the photoresist material is not rendered soluble so that it can be eliminated from the open areas.
A variety of techniques that have been proposed to shield the photoresist material from airborne chemically-basic contaminants. One technique is to carbon filter the air that is present over the IC structures during fabrication processing. This technique is somewhat effective against airborne chemically-basic contaminants. Another technique is to add an acid containing polymer material in a layer on top of the photoresist to shield it from the airborne basic contaminants. The acid containing polymer layer neutralizes the chemically-basic contaminants which may diffuse into the photoresist material.
SUMMARY OF THE INVENTION
The present invention is founded on the discovery that certain structures involved in the fabrication of modern ICs emit chemically-basic contaminants, such as ammonia, during the course of fabrication. For example, one source of ammonia contaminants is the electrical conductors formed in multiple layers of metal interconnects. Metal interconnect layers are layers of individual electrical connectors which are formed above a substrate of the IC, which route electrical signals to the components of the IC. The metal interconnect layers are vertically separated from one another by a layer of dielectric insulation, and the individual electrical conductors of each interconnect layer are horizontally spaced from one another, also by dielectric insulation. Indeed, the ability to incorporate significant numbers of multiple metal interconnects layers, with each layer having close resolution of the individual conductors, has itself contributed to the evolution and miniaturization of modern ICs.
The metal structure from which the individual conductors of each metal interconnect layers are formed includes an anti-reflective barrier layer. The anti-reflective characteristics of the layer inhibit reflection of the photoresist exposure light from the metal surfaces onto areas of the photoresist material which are not desired to be exposed. The barrier characteristics create an electrically-conductive but chemically-resistant separation of one interconnect level from the next interconnect layer, so that the chemistry of one la
Dou Shumay X.
Pasch Nicholas F.
Yates Colin
Hamilton Cynthia
John R. Ley, L.L.C.
LSI Logic Corporation
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