Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-04-24
2003-09-23
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S322000, C430S394000
Reexamination Certificate
active
06623895
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the design of photomasks (“masks”) for use in lithography, and more particularly, to the use of a hybrid mask which provides for the formation of both phase-shifted and non-phase-shifted features with a single exposure.
The present invention also relates to the use of such a mask in a lithographic apparatus, comprising for example:
a radiation system for supplying a projection beam of radiation;
a mask table for holding the mask;
a substrate table for holding a substrate; and
a projection system for projecting at least part of a pattern on the mask onto a target portion of the substrate.
BACKGROUND OF THE INVENTION
Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the mask may contain a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion in one go; such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatus—commonly referred to as a step-and-scan apparatus—each target portion is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction (the “scanning” direction) while synchronously scanning the substrate table parallel or anti-parallel to this direction; since, in general, the projection system will have a magnification factor M (generally<1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be gleaned, for example, from U.S. Pat. No. 6,046,792, incorporated herein by reference.
In a manufacturing process using a lithographic projection apparatus, a mask pattern is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging step, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemo-mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book “Microchip Fabrication: A Practical Guide to Semiconductor Processing”, Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4, incorporated herein by reference.
For the sake of simplicity, the projection system may hereinafter be referred to as the “lens”; however, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a “lens”. Further, the lithographic apparatus may be of a type having two or more substrate tables (and/or two or more mask tables). In such “multiple stage” devices the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Twin stage lithographic apparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO 98/40791, incorporated herein by reference.
Although specific reference may be made in this text to the use of lithographic apparatus and masks in the manufacture of ICs, it should be explicitly understood that such apparatus and masks have many other possible applications. For example, they may be used in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “reticle”, “wafer” or “die” in this text should be considered as being replaced by the more general terms “mask”, “substrate” and “target portion”, respectively.
In the present document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g. with a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultra-violet radiation, e.g. having a wavelength in the range 5-20 nm).
U.S. Pat. No. 5,340,700 (incorporated herein by reference) describes a method of printing sub-resolution features defined by image decomposition. More specifically, the method discloses first decomposing the sub-resolution features into much larger features such that the feature edges are separated far enough from each other so that the aerial images of the feature edges are “non-correlated” to one another. In other words, the edges are optically “isolated.” By exposing such a decomposed mask with pre-determined multiple exposure steps, it was shown that near-half-wavelength contact hole features can be well defined. For printing line features, the method of U.S. Pat. No. 5,340,700 utilizes negative-acting photoresist, because as the negative-acting photoresist has inherently poorer resolution, the multiple exposure, image de-composition method is best suited for printing contact hole features. Although it has very high printed resolution potential, the method disclosed in U.S. Pat. No. 5,340,700 has not yet been widely adopted in the industry, mainly due to the relative complexity of decomposing the images. Moreover, any method utilizing multiple exposure masking steps negatively impacts the throughput of the lithographic exposure apparatus.
In recent years, the phase-shift mask (“PSM”) has been gradually accepted by the industry as a viable alternative for sub-exposure-wavelength manufacturing. Since the early design (Levenson et al., 1982), many forms of PSM have been developed over the years. Of those, two fundamental forms of PSM have been investigated the most, namely alternating PSM (“altPSM”) as illustrated in FIGS.
1
(
a
) and
1
(
b
) and attenuated PSM (“attPSM”) as illustrated in FIG.
2
.
From the image formation point of view, for approximately a 1:1 ratio of line:space features, altPSM eliminates the 0
th
diffraction order and forms the image pattern with two beams, namely +/−1
st
diffraction orders. This type of PSM is also referred to as “strong” PSM. “Weak” PSM refers to the existence of a 0
th
diffraction order component for image formation. The stronger the PSM, the smaller the 0
th
diffraction order component, and vice versa. In theory, altPSM can form image patterns at double the original spatial frequencies. Hence, pattern resolution can be twice as fine. AltPSM is often referred to as “strong” PSM since it offers the best resolution improvement potential. To achieve the highest possible resolution p
Caldwell Roger
Chen Jang Fung
Laidig Thomas
Wampler Kurt E.
ASML Masktools Netherlands B.V.
Rosasco S.
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