Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2002-02-06
2004-05-11
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S030000, C716S030000
Reexamination Certificate
active
06733929
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to manufacturing small dimension features of objects, such as integrated circuits, using photolithographic masks. More particularly, the present invention relates to the application of phase shift masking to complex layouts for integrated circuits and similar objects.
2. Description of Related Art
Phase shift masking, as described in U.S. Pat. No. 5,858,580, has been applied to create small dimension features in integrated circuits. Typically the features have been limited to selected elements of the design, which have a small, critical dimensions. Although manufacturing of small dimension features in integrated circuits has resulted in improved speed and performance, it is desirable to apply phase shift masking more extensively in the manufacturing of such devices. However, the extension of phase shift masking to more complex designs results in a large increase in the complexity of the mask layout problem. For example, when laying out phase shift areas on dense designs, phase conflicts will occur. One type of phase conflict is a location in the layout at which two phase shift windows having the same phase are laid out in proximity to a feature to be exposed by the masks, such as by overlapping of the phase shift windows intended for implementation of adjacent lines in the exposure pattern. If the phase shift windows have the same phase, then they do not result in the optical interference necessary to create the desired effect. Thus, it is necessary to prevent inadvertent layout of phase shift windows in phase conflict.
Another problem with laying out complex designs which rely on small dimension features, arises because of isolated exposed spaces which may have narrow dimension between unexposed regions or lines. Furthermore, proximity effects including optical proximity effects, resist proximity effects, and etch proximity effects, can have greater impact on the layout of dense, small dimension patterns.
Because of these and other complexities, implementation of a phase shift masking technology for complex designs will require improvements in the approach to the design of phase shift masks, and new phase shift layout techniques.
SUMMARY OF THE INVENTION
The present invention provides techniques for extending the use of phase shift techniques to implementation of masks for complex layouts in the layers of integrated circuits, beyond selected critical dimension features such as transistor gates to which such structures have been limited in the past. The invention provides a method that includes identifying features for which phase shifting can be applied, automatically mapping the phase shifting regions for implementation of such features, resolving phase conflicts which might occur according to a given design rule, applying assist features, and adjusting for proximity correction shapes within phase shift windows and within trim mask shapes associated with the phase shift windows. The present invention is particularly suited to opaque field phase shift masks which are designed for use in combination with trim masks for clearing unwanted artifacts of the phase shift masking step, and optionally defining interconnect structures and other types of structures, necessary for completion of the layout of the layer.
In one embodiment, the process of identifying features suitable for implementation using phase shifting includes reading a layout file which identifies features of the complex pattern to be exposed.
In one preferred embodiment, the phase shift mask includes an opaque field, and the phase shift regions include a plurality of transparent windows having a first phase within the opaque field, and a plurality of complementary transparent windows having a second phase approximately 180 degrees out of phase with respect to the first phase, within the opaque field. The opaque field leaves unexposed lines formed using the phase transition between phase shift regions unconnected to other structures in some cases. A complementary trim mask is laid out for use is conjunction with the opaque field phase shift mask. In one embodiment, the complementary trim mask is a binary mask, without phase shifting features. In other embodiments, the trim masks include various combinations of binary features, tri-color features, phase shift features, attenuated phase shift features and attenuated-opacity trim features.
The present invention provides a method for laying out an opaque field, alternating phase shift mask pattern and a trim mask pattern for use with the phase shift mask pattern to produce a target feature, and providing for proximity adjustments, including but not limited to optical proximity correction OPC adjustments, to the patterns. The phase shift mask pattern includes a first phase shift window having a first side and a second side opposite the first time and spaced away from the first side by a phase shift window width, a second phase shift window having a first side and a second side opposite the first side and spaced away from the first side by a phase shift window width, and an opaque field referred to sometimes as “control chrome,” having a control width, overlying the region of phase transition along the respective first sides in between the first and second phase shift windows. The trim mask pattern includes an opaque trim shape in a location corresponding with said region of phase transition and having a trim width in the dimension parallel with said control width. According to the present invention, an adjustment for proximity effects, is applied to at least one, and preferably both, of the phase shift mask pattern and the trim mask pattern based upon one or both of the rule based correction and a model based correction to improve a match between resulting exposure pattern and a target feature. In one embodiment, the adjustment includes one, or more than one, of the following process steps:
(1) adjusting said first phase shift window width and said second phase shift window width,
(2) adjusting said control width,
(3) adjusting said trim width,
(4) adding a sub-resolution opaque shape to one or both of the first and second phase shift windows,
(5) adding a clear shape to the trim shape, and
(6) adding one or more opaque shapes to one or both of the first and second phase shift windows and adding a clear shape or shapes to the trim mask pattern, where
(i) the opaque shapes in the phase shift windows are at or above resolution, and clear shapes in the trim shape are below resolution in one embodiment, and are at or above resolution in another embodiment, and
(ii) the opaque shapes in the phase shift windows are below resolution, and clear shapes in the trim shape are below resolution in one embodiment, and are at or above resolution in another embodiment.
The sub-resolution shapes do not “print” in the image being exposed, but affect the intensity profile at the wafer level, such as by improving contrast of the image and thereby improving process latitude, and changing the size of the printed image caused by the phase shift region in which the sub-resolution feature is laid out, such as for optical proximity correction OPC.
As a result of the layout rule, regions in the phase shift mask may result in phase conflicts. Thus, embodiments of the invention also include applying an adjustment to one or more of the phase shift regions in the phase shift mask to correct for phase conflicts. The adjustment for phase conflicts in one embodiment comprises dividing a phase shift region having a first phase into a first phase shift region having the first phase in a second phase shift region having the second phase. An opaque feature is added to the phase shift mask between the first and second phase shift regions. The complementary mask includes a corresponding opaque feature preventing exposure of the features to be exposed using the first and second phase shift regions in the phase shift mask, and includes a cut-out over the opaque feature separating the first and second phase shift regions to expose
Haynes Mark A.
Haynes Beffel & Wolfeld LLP
Huff Mark F.
Mohamedulla Saleha R.
Numerical Technologies Inc.
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