Active solid-state devices (e.g. – transistors – solid-state diode – Specified wide band gap semiconductor material other than...
Reexamination Certificate
1998-08-14
2001-10-02
Mintel, William (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Specified wide band gap semiconductor material other than...
C257S077000, C257S436000, C257S437000, C257S635000, C257S637000, C438S763000, C438S781000, C438S931000, C438S952000
Reexamination Certificate
active
06297521
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to integrated circuits, and particularly, but not by way of limitation, to a graded silicon oxycarbide anti-reflective coating for integrated circuit photolithography.
BACKGROUND OF THE INVENTION
Trends in modern integrated circuit (IC) technology demand increasingly dense ICs, such as for computer systems, portable electronics, and telecommunications products. IC fabrication includes, among other things, photolithography for selective patterning and etching of photoresist layers. The patterned photoresist layer serves as a masking layer such that a subsequent IC processing step is carried out on only those portions of the underlying IC that are uncovered by photoresist, as described below.
A photoresist layer is typically formed on an underlying integrated circuit substrate. The photoresist layer overlays any structures that are already formed on the substrate. Portions of the photoresist are selectively exposed to light through a lithographic mask that includes clear and opaque portions forming a desired pattern. Light is transmitted through the clear portions of the mask, but not through the opaque portions. The incident light changes the chemical structure of the exposed portions of photoresist. A chemical etchant, which is sensitive to only one of the exposed and unexposed portions of the photoresist, is applied to the photoresist to selectively remove those portions of the photoresist to which the chemical etchant is sensitive. As a result, portions of the photoresist which are insensitive to the chemical etchant remain on the IC. The remaining portions of the photoresist protect corresponding underlying portions of the IC from a subsequent IC processing step. After this IC processing step, the remaining portions of the photoresist layer are typically removed from the IC.
High density ICs require sharply defined photoresist patterns, because these patterns are used to define the locations (and density) of structures formed on the IC. However, light reflects from the surface of the underlying substrate on which the photoresist is formed. Certain structures that are formed on the underlying substrate are highly reflective such as, for example, aluminum layers for forming circuit interconnections. Reflections from the surface of the substrate underlying the photoresist causes deleterious effects that limit the resolution of photolithographic photoresist patterning, as described below.
First, reflections cause the light to pass through the photoresist at least twice, rather than only once. In other words, light first passes through the photoresist to reach the surface of the underlying substrate. Then, light is reflected from the surface of the underlying substrate and passes back through the photoresist layer a second time. The chemical structure of the photoresist changes differently when light passes through the photoresist more than once, rather than when light passes through the photoresist only once. A portion of the light, already reflected from the surface of the underlying substrate, can also reflect again from the surface of the photoresist, passing back through the photoresist yet again. In fact, standing light waves can result in the photoresist from superpositioning of incident and reflected light rays. This overexposure problem is sometimes referred to as the “swing effect.”
Even more problematic, the reflections of the light are not necessarily perpendicular. Light reflects angularly from the surface of the underlying substrate. even if the light is incident exactly perpendicular to the surface of the substrate. This results from the diffractive nature of light (i.e., light bends). Off-angle reflections reduce the sharpness of the resulting photoresist pattern. A portion of the light reflected obliquely from the surface of the underlying substrate can also be again reflected obliquely from the surface of the photoresist. As a result of such angular reflections, the light can travel well outside those photoresist regions underlying the transmissive portions of the photolithographic mask. This potentially causes photoresist exposure well outside those photoresist regions underlying transmissive portions of the photolithographic mask. This problem, which is some times referred to as “notching,” results in a less sharply defined photoresist pattern that limits the density of structures formed on the integrated circuit. There is a need to overcome these photolithographic limitations to obtain the benefits of high resolution photolithography and high density integrated circuits.
SUMMARY OF THE INVENTION
The present invention provides, among other things, an antireflective coating (ARC), such as for use in integrated circuit (IC) photolithography. In one embodiment, the invention provides an antireflective structure that includes a first layer formed on the substrate. A second layer is formed on the first layer. The second layer has a working surface for receiving a photoresist layer formed thereupon. An optical impedance of the second layer, at an interface between the first and second layers, is approximately equal to an optical impedance of the first layer. The optical impedance of the second layer increases in a direction away from the interface between the first and second layers. The optical impedance at the working surface of the second layer is approximately equal to the optical impedance of at least a portion of the photoresist layer.
In another embodiment, the present invention provides, among other things, an integrated circuit. The integrated circuit includes a first layer, having a first optical impedance, formed on a substrate. A second layer, having a second optical impedance, is formed on the first layer. The second layer has a gradient optical impedance. A photoresist layer, having a photoresist optical impedance, is formed on the second layer.
In another embodiment, the present invention provides, among other things, a gradient antireflective coating for an integrated circuit. The coating includes an optically absorptive first layer formed on an integrated circuit substrate. A second layer is formed between the first layer and a photoresist layer. The second layer has an optical impedance approximately equal to an optical impedance of the first layer. The optical impedance of the second layer increases in a direction away from the interface between the first and second layers.
In another embodiment, the present invention provides, among other things, an antireflective structure that includes a first layer formed on the substrate. A second layer is formed on the first layer. The second layer has a working surface for receiving a photoresist layer formed thereupon. A composition of the second layer, at an interface between the first and second layers, is approximately equal to a composition of the first layer, at an interface between the first and second layers. The composition of the second layer changes in a direction away from the interface between the first and second layers.
Another aspect of the present invention provides a method. A first layer is formed on an integrated circuit substrate. A second layer is formed on the first layer. A composition of at least a portion of the second layer is graded in a direction away from an interface between the first and second layers. A photoresist layer is formed on the second layer. The substrate is exposed to incident light. Substantially all of the incident light that reaches the first layer is absorbed in the first layer.
In one embodiment, by way of example, but not by way of limitation, the present invention provides a method of forming an antireflective coating on a substrate. A silicon carbide first layer is formed on the substrate. A substantially continuously graded composition silicon oxycarbide second layer is formed on the first layer. A portion of the second layer that is adjacent to the first layer has a material composition that approaches that of silicon carbide.
Thus, the present invention provides, among other things, an
Ahn Kie Y.
Forbes Leonard
Micro)n Technology, Inc.
Mintel William
Schwegman Lundberg Woessner & Kluth P.A.
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