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METHOD OF INSPECTION, A METHOD OF
MANUFACTURING, AN INSPECTION
APPARATUS, A SUBSTRATE, A MASK, A
LITHOGRAPHY APPARATUS AND A
LITHOGRAPHIC CELL 5
The present invention relates to methods of inspection usable, for example, in the manufacture of devices by litho- 10 graphic techniques and to methods of manufacturing devices using lithographic techniques.
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred 20 to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a 25 layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire 30 pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the "scanning"-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also pos- 35 sible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In order to monitor the lithographic process, it is necessary to measure parameters of the patterned substrate, for example the overlay error between successive layers formed in or on it. 40 There are various techniques for making measurements of the microscopic structures formed in lithographic processes, including the use of scanning electron microscopes and various specialized tools. One form of specialized inspection tool is a scatterometer in which a beam of radiation is directed 45 onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it has been reflected or scattered by the substrate, the properties of the substrate can be determined. This can be done, for example, 50 by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. Two main types of scatterometer are known. Spectroscopic scatterometers direct a broadband radiation beam onto the substrate and measure the spectrum (intensity as a 55 function of wavelength) of the radiation scattered into a particular narrow angular range. Angularly resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.
Such a system of illuminating a target and collecting data 60 from the reflected radiation is often used to calculate the overlay error, OV for a pattern. This can be achieved by forming a plurality of superimposed gratings on the substrate and measuring the overlay error between the gratings. To measure the overlay in, for example, the X direction, a grating 65 varying in the X direction, as shown in FIG. 9a of the accompanying drawings is used. To measure overlay in, for
example, the Y direction, a grating varying in the Y direction, as shown in FIG. 9b of the accompanying drawings is used. Each of these targets occupies an area on the substrate that could otherwise be used for other patterns, such as those that form the basis for an integrated circuit, and thus occupies valuable space.
An alternative target pattern is shown in FIG. 10 of the accompanying drawings. In this target, the pattern varies in both the X and Y direction and therefore only one target is used. However, cross-talk between the X and Y directions occurs when this target is used, thus reducing the accuracy of the results and increasing the complexity of the computation of the results.
It is desirable to provide an alternative target in which both the area of the substrate used and cross-talk are minimized.
According to an embodiment of the invention, there is provided a method of inspection to determine the overlay error in a substrate including projecting a beam of radiation onto a target on the substrate, measuring the reflected radiation reflected from the target on the substrate using a scatterometer; and determining the overlay error from the reflected radiation; wherein the target includes first and second overlapping patterns, each pattern including a first sub-pattern having features which vary only in a first direction and a second sub-pattern having features which vary only in a second direction, the target being arranged to determine the overlay in a plurality of direction within a single measurement.
According to an embodiment of the invention there is provided an inspection apparatus configured to measure a property of a substrate, the apparatus including: a radiation projector configured to project radiation on to a target on the substrate; a detector configured to detect the radiation reflected from the target; a data handling unit, wherein the data handling unit is configured to calculate the overlay error in two directions from the radiation reflected from a single target including first and second overlying patterns, each including a first portion including a sub-pattern which varies only in a first direction and a second portion including a sub-pattern which varies only in a second direction.
According to an embodiment of the invention there is provided a substrate having printed thereon a target to be used to determine the overlay in a plurality of directions within a single measurement, the target including first and second overlying patterns, each including a first sub-pattern having features which vary only in a first direction and a second sub-pattern having features which vary only in a second direction.
According to an embodiment of the invention there is provided a mask for use in printing a target on a substrate, the mask including a pattern representing a target including first and second overlying patterns, each including a first subpattern having features which vary only in a first direction and a second sub-pattern having features which vary only in a second direction.
According to an embodiment of the invention, there is provided a lithographic apparatus including an illumination system configured to condition a beam of radiation; a support configured to hold a patterning device, the patterning device configured to pattern the beam of radiation to form a patterned beam of radiation; a substrate table configured to support a substrate; a projection system configured to project the patterned beam of radiation onto the substrate; and an inspection apparatus configured to measure a property of the substrate,
the inspection apparatus including a radiation projector configured to project radiation on to a target on the substrate; a detector configured to detect the radiation reflected from the target; a data handling unit configured to calculate an overlay error in two directions from the radiation reflected from a 5 single target including first and second overlying patterns, each pattern comprising a first portion including a sub-pattern which varies only in a first direction and a second portion including a sub-pattern which varies only in a second direction. 10
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying 15 schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
FIG. la depicts a lithographic apparatus in accordance with an embodiment of the invention;
FIG. lb depicts a lithographic cell or cluster in accordance 20 with an embodiment of the invention;
FIG. 2 depicts a scatterometer in accordance with an embodiment of the invention;
FIG. 3 depicts a scatterometer in accordance with an embodiment of the invention; 25
FIG. 4 depicts a target according to an embodiment of the invention;
FIG. 5 depicts a detailed view of an arrangement of target sites according to an embodiment of the invention;
FIGS. 6a-b depict an alternative target according to an 30 embodiment of the invention;
FIGS, la-b depict an alternative target according to an embodiment of the invention;
FIGS. 8a-b depict an alternative target according to an embodiment of the invention; 35
FIGS. 9a-b depict a conventional target; and
FIG. 10 depicts a conventional target.
FIG. la schematically depicts a lithographic apparatus. The apparatus includes an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or EUV radiation); a support structure (e.g. amasktable) MT constructed to support a patterning device (e.g. a mask) 45 MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accu- 50 rately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PL configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. including one or more dies) of the substrate W. 55
The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. 60
The support structure supports, i.e. bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is 65 held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping tech
niques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms "reticle" or "mask" herein may be considered synonymous with the more general term "patterning device."
The term "patterning device" used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam, which is reflected by the mirror matrix.
The term "projection system" used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered as synonymous with the more general term "projection system".
As here depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask).
The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such "multiple stage" machines 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 exposure.
The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the patterning device (e.g. mask) and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term "immersion" as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.
Referring to FIG. la, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the