KR101330116B1 - Method of determining a characteristic - Google Patents

Abstract

The first target population and the second target population are etched into the substrate. The second target population is asymmetrical with respect to the first target population. This may allow different target populations to be distinguished and the characteristics of the different target populations to be determined.

Description

How to determine the attribute {METHOD OF DETERMINING A CHARACTERISTIC}

This application claims the benefit of US Provisional Application No. 61 / 141,414, filed December 30, 2008, which is incorporated herein in its entirety.

The present invention relates to a method of determining the properties of a substrate.

A lithographic apparatus is a machine that applies a desired pattern onto a substrate, typically onto a target portion of the substrate. The lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). In that case, a patterning device, alternatively referred to as a mask or a reticle, can be used to create a circuit pattern to be formed on a separate layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of one or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically performed through imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will comprise 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 pattern onto the target portion at one time, and scanning the pattern through a radiation beam in a given direction ("scanning" -direction) Called scanner, in which each target portion is irradiated by synchronously scanning the substrate in a direction parallel (parallel to the same direction) or in a reverse-parallel direction (parallel to the opposite direction). It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern on the substrate.

In order to monitor the lithography process, it is necessary to measure the parameters of the patterned substrate, for example the overlay error between successive layers formed in or on the substrate. A variety of techniques exist, including scanning electron microscopy and the use of various specialized tools, to perform measurements of microscopic structures formed during the lithography process. One form of special inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and the properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after the beam is reflected or scattered by the substrate, the properties of the substrate can be determined. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. Two main forms of the scatterometer are known. A spectroscopic scatterometer directs a broadband beam of radiation onto a substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered in a particular narrow angular range. An angularly resolved scatterometer uses a monochromatic radiation beam and measures the intensity of the scattered radiation as a function of angle.

Fabrication of IC chips involves fabrication of multiple layers. In order to create a more detailed pattern, a plurality of lithography and etching process steps can be used in the manufacture of each layer: this is known as double patterning. There are a number of different ways of achieving double patterning. One of these methods is known as lithographic-etch-lithography-etch (LELE), in which case the first pattern is exposed and etched. Thereafter, the second pattern with features located in the spaces between the features of the first pattern is exposed and etched. Accordingly, a pattern of smaller dimensions can be created. Another similar double patterning technique is known as lithography-freeze-lithography-etch (LFLE). After the pattern is exposed in the resist, it is frozen. Thereafter, a second pattern may also be exposed in the resist, after which the two patterns are etched into the substrate. Another double patterning method is known as the spacer method. In the spacer method, a sacrificial template is placed and spacers are placed adjacent to both sides of the sacrificial template. The template is then removed and the resulting pattern is etched into the substrate.

If two lithographic steps are used to create a single pattern, there may be some errors in the placement of the features, for example in the second lithography step. Similarly, the features exposed during the first lithography step may not be the same as the features exposed during the second lithography step. Since there were two lithography steps, the features exposed during each lithography step may be different and may need to be evaluated separately. However, since the features exposed during the first and second lithography steps necessarily form very similar and regular patterns, it may be difficult to distinguish between two sets of features using angularly resolved scatterometry.

In spacer technology, spacers are used to create a regular pattern. However, if the spacer is too large or too small, the pattern will be irregular. Similarly, the pattern may be nearly irregular, but it will be difficult to evaluate small irregularities in the pattern.

In order to evaluate the exposed features in each of the exposure steps, SEM was used previously. However, SEM is not fast enough to maintain the throughput of the substrate in high volume manufacturing of IC chips.

Therefore, there is a need for an improved method of evaluating features used in double patterning techniques.

In one embodiment of the present invention, there is provided a method of determining characteristics of an inspection apparatus, a lithographic cell or a lithographic apparatus configured to measure a property of a substrate, a first population or a second population of features on a substrate,

The first and second populations are nominally (eg, substantially) identical and form (eg, produce) a single pattern within a single layer on a substrate, the pattern being in combination with the features of the first population. Has a period equal to the distance between the nearest features of the second population,

The method comprising:

Forming a first population on the substrate, the first population comprising a first target population;

Forming a second population on the substrate, the second population comprising a second target population, wherein the second target population and the first target population form a combined target population;

Detecting radiation reflected from the combined target population; And

Calculating a characteristic of said first population or said second population using radiation reflected from said target,

The second target population is asymmetrical with respect to the first target population.

Further embodiments, features, and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. In the present specification, these embodiments are presented for illustrative purposes only. Those skilled in the art will apparently appreciate further embodiments based on the teachings contained herein.

DETAILED DESCRIPTION OF THE EMBODIMENTS Hereinafter, embodiments of the present invention will be described only by way of example with reference to the accompanying drawings in which corresponding reference numbers indicate corresponding parts. In addition, the accompanying drawings, which are incorporated in and form a part of the specification, illustrate the invention, together with the description serve to explain the principles of the invention and to enable those skilled in the art to make and use the invention:
1 illustrates a lithographic apparatus according to one embodiment of the present invention;
2 shows a lithographic cell or cluster according to an embodiment of the present invention;
3 shows a first scatterometer according to an embodiment of the present invention;
4 shows a second scatterometer according to an embodiment of the present invention;
5 illustrates a pattern exposed using a double patterning technique in accordance with one embodiment of the present invention;
6 is a graph showing how the intensity of a zeroth order diffraction pattern changes with overlay error, according to an embodiment of the invention;
FIG. 7A illustrates a pattern in which an overlay error exists between a first population and a second population, in accordance with an embodiment of the present invention; FIG.
FIG. 7B illustrates a target population in which there is an overlay error and bias between the first target population and the second target population, in accordance with an embodiment of the present invention; FIG.
8A illustrates steps and resulting patterns in a spacer patterning technique, in accordance with an embodiment of the present invention;
FIG. 8B illustrates the steps in the manufacture of a target using spacer patterning techniques and the resulting target, in accordance with an embodiment of the invention; FIG.
9 illustrates a target made in accordance with one embodiment of the present invention;
10 illustrates another target according to an embodiment of the present invention; And
11 illustrates a target according to an embodiment of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify corresponding elements throughout. In the drawings, like reference numerals generally refer to the same, functionally similar, and / or structurally similar elements. The drawing where the element first appears is indicated by the first number (s) of the corresponding reference number.

The present specification discloses one or more embodiments that incorporate the features of the present invention. The disclosed embodiment (s) merely illustrate the present invention. The scope of the invention is not limited to the disclosed embodiment (s). The invention is defined by the claims appended hereto.

In the present specification, the embodiment (s) described in the context of "one embodiment", "one embodiment", "exemplary embodiment", and the like, Features, but it should be understood that not all embodiments necessarily include a particular feature, structure, or characteristic. Further, such phrases do not necessarily refer to the same embodiment. In addition, where a particular feature, structure, or characteristic is described in connection with one embodiment, it is understood that it is within the knowledge of a person skilled in the art whether it is clearly described or not affecting this feature, structure or characteristic in connection with other embodiments. I understand.

Embodiments of the invention may be implemented in hardware, firmware, software or any combination thereof. In addition, embodiments of the present invention may be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. Machine-readable media may include any mechanism for storing or transmitting information in a form readable by a machine (eg, a computing device). For example, the machine-readable medium may include read only memory (ROM); Random access memory (RAM); Magnetic disk storage media; Optical storage media; Flash memory devices; Electrical, optical, acoustical or other forms of propagated signals (eg, carrier waves, infrared signals, digital signals, etc.) and the like. In addition, firmware, software, routines, and instructions may be described herein as performing certain operations. However, it is to be understood that these descriptions are for convenience only, and that the operation may in fact occur from a computing device, a processor, a controller, or another device executing firmware, software, routines, instructions, or the like.

However, before describing these embodiments in more detail, it is advantageous to present an exemplary environment in which embodiments of the present invention may be implemented.

Figure 1 schematically depicts a lithographic apparatus. The lithographic apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B (eg UV radiation or DUV radiation); A support structure (e.g., a mask table) MA constructed to support a patterning device (e.g., mask) MA and coupled to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters ) (MT); A substrate table (e.g., a wafer table) configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate according to certain parameters, Wafer table) WT; And a projection system (e.g., a projection system) configured to project a pattern imparted to the radiation beam B by a patterning device MA onto a target portion C (e.g. comprising one or more dies) (E.g., a refractive projection lens system) PL.

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 have.

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 held in a vacuum environment. The support structure may utilize mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device. The support structure may be, for example, a frame or a table that may be fixed or movable as required. The support structure can 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 " as used herein should be broadly interpreted as referring to any device that can be used to impart a pattern to a cross-section of a radiation beam to create a pattern in a target portion of the substrate. The pattern imparted to the radiation beam may be precisely matched to the desired pattern in the target portion of the substrate, for example when the pattern comprises phase-shifting features or so-called assist features . Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in the device to be 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 the lithographic arts and include mask types such as binary, alternating phase-shift and attenuated phase-shift, and various hybrid mask types. One example of a programmable mirror array employs a matrix configuration of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam 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, catadioptric, catadioptric, But should be broadly interpreted as including any type of projection system, including magnetic, electromagnetic and electrostatic optical systems, or any combination thereof. Any use of the term "projection lens" herein may be considered as synonymous with the more general term "projection system ".

As shown herein, 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 the type as mentioned above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (e.g., dual stage) or more substrate tables (and / or two or more mask tables). In such "multiple stage" machines, additional substrate tables may be used in parallel, or preparatory steps may be performed on one or more other tables while one or more tables are being used for exposure.

The lithographic apparatus may also be of a type wherein all or a portion of the substrate may be covered with a liquid, e.g., water, having a relatively high refractive index, to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of a projection system. The term "immersion " as used herein does not mean that a structure such as a substrate has to be immersed in liquid, but rather means that the liquid only has to lie between the projection system and the substrate during exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from a radiation source SO. For example, where the source is an excimer laser, the source and the lithographic apparatus may be separate entities. In this case, the source is not considered to form part of the lithographic apparatus, and the radiation beam is incident on the source (e.g., with the aid of a beam delivery system BD including, for example, a suitable directional mirror and / or a beam expander) SO) to the illuminator IL. In other cases, for example when the source is a mercury lamp, the source may be an integral part of the lithographic apparatus. The source SO and the illuminator IL may be referred to as a radiation system together with a beam delivery system BD if necessary.

The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as -outer and -inner, respectively) of the intensity distribution in the pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam to have a desired uniformity and intensity distribution in the cross section of the radiation beam.

The radiation beam B is incident on the patterning device (eg mask) MA, which is held on the support structure (eg mask table) MT, and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PL, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and the position sensor IF (e.g. interferometric device, linear encoder, 2-D encoder or capacitive sensor), the substrate table WT is moved, for example, B to position different target portions C in the path of the target portion C. Similarly, the first positioner PM and another position sensor (not explicitly shown in FIG. 1), for example, after mechanical retrieval from a mask library or during scanning It can be used to accurately position the mask MA with respect to the path of the beam B. In general, the movement of the mask table MT may be realized with the aid of a long-stroke module and a short-stroke module, 1 positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form a part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT may only be connected or fixed to the short-stroke actuators. The mask MA and the substrate W may be aligned using the mask alignment marks M1 and M2 and the substrate alignment marks P1 and P2. Although the substrate alignment marks illustrated occupy dedicated target portions, they may be located in the spaces between the target portions (these are known as scribe-lane alignment marks). Similarly, in situations where more than one die is provided on the mask MA, the mask alignment marks may be located between the dies.

The lithographic apparatus may be used in at least one of the following modes:

1. In the step mode, the mask table MT and the substrate table WT are basically kept stationary, while the entire pattern imparted to the radiation beam is projected onto the target portion C at once (ie, a single static Single static exposure]. The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged during a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i. E., A single dynamic exposure )]. The speed and direction of the substrate table WT relative to the mask table MT may be determined by the magnification (image reduction) and image reversal characteristics of the projection system PL. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion during a single dynamic exposure, while the length of the scanning operation determines the height of the target portion (in the scanning direction).

3. In another mode, the mask table MT is kept essentially stationary holding a programmable patterning device, and while the pattern imparted to the radiation beam is projected onto the target portion C, the substrate table WT Is moved or scanned. In this mode, a pulsed radiation source is generally employed, and the programmable patterning device is updated as needed after each movement of the substrate table WT, or between successive radiation pulses during a scan . This mode of operation can be readily applied to maskless lithography using a programmable patterning device, such as a programmable mirror array of a type as referred to above.

Combinations and / or variations on the above described modes of use, or entirely different modes of use, may also be employed.

As shown in Figure 2, the lithographic apparatus LA sometimes forms a portion of a lithography cell LC, also referred to as a lithocell or cluster, which is pre-exposed and post- And an apparatus for performing post-exposure processes. Typically, they include a spin coater (SC) for depositing resist layers, a developer (DE) for developing exposed resist, a chill plate (CH) and a bake plate (BK) do. After the substrate handler or robot RO picks up the substrates from the input / output ports I / O1 and I / O2 and moves the substrates between different processing apparatuses, the loading bay of the lithographic apparatus: LB). These devices, often collectively referred to as tracks, are under the control of a track control unit (TCU), which is controlled by a supervisory control system (SCS) that controls the lithographic apparatus through a lithographic control unit (LACU). Thus, different devices can be operated to maximize throughput and processing efficiency.

In order for the substrates exposed by the lithographic apparatus to be correctly and consistently exposed, it is desirable to inspect the exposed substrates to measure properties such as overlay error, line thickness, critical dimension (CD), etc. between subsequent layers. If an error is detected, adjustments can be made to the exposure of subsequent substrates, particularly if the inspection can be done quickly enough so that another substrate of the same batch is still exposed. In addition, substrates that have already been exposed can be avoided, for example, stripping to improve yield, reworked, or discarded to perform exposure on substrates known to be defective. If only some target portions of the substrate are defective, another exposure may be performed on only good target portions.

The inspection apparatus is used to determine the characteristics of the substrate, and in particular is used to determine how the characteristics of different substrates or of different layers of the same substrate vary from layer to layer. The inspection apparatus may be integrated into the lithographic apparatus LA or the lithocell LC, or it may be a stand-alone device. To enable the quickest measurements, the inspection apparatus preferably measures the properties in the exposed resist layer immediately after exposure. However, the latent image in the resist has a very low contrast such that there is only a very small difference in the refractive index between the portion of the resist exposed to the radiation and the portion of the unexposed resist, and all inspection apparatuses It does not have sufficient sensitivity to make useful measurements. Therefore, measurements may be performed after the post-exposure bake step (PEB), which is the first step usually performed on the exposed substrate and increases the contrast between the exposed and unexposed portions of the resist. At this stage, the image in the resist may be referred to as semi-latent. It is also possible to perform measurements of the developed resist image, in which either the exposed or unexposed portions of the resist have been removed, or it may be performed after a pattern transfer step such as etching. The latter possibility limits the possibility of reprocessing the defective substrate, but it can still provide useful information.

Figure 3 illustrates a scatterometer that may be used in an embodiment of the present invention. Which includes a broadband (white light) radiation projector 2 for projecting radiation onto a substrate W. The reflected radiation is passed through a spectrometer detector 4 which measures the spectrum 10 (intensity as a function of wavelength) of specular reflected radiation. From this data, the profile or structure produced by the detected spectrum can be simulated, for example, by Rigorous Coupled Wave Analysis (RCWA) and non-linear regression, or as shown at the bottom of FIG. 3. By comparing with the library of the spectra, it can be reconstructed by the processing unit (PU). In general, the general form of the structure is known for reconstruction, and some parameters are assumed from the knowledge of the process in which the structure is made, leaving only a few parameters of the structure to be determined from the scatterometry data. Such a scatterometer may be configured as a normal-incidence scatterometer or an oblique-incidence scatterometer.

Another scatterometer that can be used with the present invention is shown in FIG. In this device, the radiation emitted by the radiation source 2 is focused using the lens system 12, through an interference filter 13 and a polarizer 17, in partially Reflected by the reflected surface 16, it is focused onto the substrate W through a microscope objective lens 15 having a high numerical aperture NA of at least about 0.9 and at least about 0.95, for example. The immersion scatterometer may even have a lens with a numerical aperture greater than one. The reflected radiation is then transmitted to the detector 18 through the partially reflective surface 16 so that a scatter spectrum is detected. The detector may be located in a back-projected pupil plane 11 that is present at the focal length of the lens system 15, but instead the pupil plane may be located on the detector (not shown) Or may be re-imaged onto the substrate. The pupil plane is a plane in which the radial position of the radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation. The detector is a two-dimensional detector such that the two-dimensional angular scattering spectrum of the substrate target 30 can be measured. In one example, detector 18 may be an array of CCD or CMOS sensors, for example, using an integration time of 40 milliseconds per frame.

For example, a reference beam is often used to measure the intensity of incident radiation. To this end, when the radiation beam is incident on the beam splitter 16, a part thereof is transmitted as a reference beam toward the reference mirror 14 through the beam splitter. The reference beam is then projected onto a different part of the same detector 18.

For example, one set of interference filters 13 may be used to select a wavelength of interest in the range of about 405 to 790 nm, or even lower, such as about 200 to 300 nm. . The interference filter may be tunable rather than including a set of different filters. Instead of interference filters, a grating may be used.

Detector 18 may measure the intensity of scattered light in the short or narrow wavelength range, separate intensity at multiple wavelengths, or integrated intensity over a wavelength range. In addition, the detector can separately measure the phase difference between transverse magnetic-polarization and transverse electric-polarization intensity, and / or transverse magnetic-polarization and transverse-electrical-polarization.

A broadband light source (i. E., A broad light frequency or wavelengths - and a light source with colors thereon) can be used, which provides a wide etendue to allow mixing of multiple wavelengths. The plurality of wavelengths in the wideband each have a bandwidth of Δλ and a spacing of at least 2Δλ (ie, twice the bandwidth). The plurality of "sources" of radiation may be different portions of an extended radiation source that have been split using a fiber bundle. In this way, angularly resolved scatter spectra can be measured in parallel at multiple wavelengths. For example, a 3-D spectrum such as wavelength and two different angles can be measured, which contains more information than the 2-D spectrum. This allows more information to be measured that increases the metrology process robustness. This is described in more detail in European Patent No. 1,628,164A, which is incorporated by reference in its entirety herein.

The target 30 on the substrate W may be a grating that is printed such that the bars are formed of solid resist lines after development. Alternatively, the bars can be etched into the substrate. This pattern may be sensitive to chromatic aberration and illumination symmetry in the lithographic projection apparatus, particularly in the projection system PL, and the presence of such aberrations will be evidenced by variations in the printed grating. Thus, scatterometry data of the printed grid is used to reconstruct the grids. From the information of the printing step and / or other scatterometry processes, parameters of the grating, such as line width and shape, can be input to the reconstruction process performed by the processing unit PU.

In order to distinguish the two groups used in double patterning, it is necessary to introduce a difference, or asymmetry, between the two groups. A regular pattern is shown in FIG. 5 in which both groups form the same and regular pattern. However, if there is a small overlay error between the second group and the first group, it is difficult to detect because the zero-order diffraction pattern (used in most scatterometry applications) does not substantially change. The intensity variation of the zero order diffraction pattern is shown in FIG. 6. As can be seen from FIG. 6, for a given change in overlay error for a small overlay error, the change in diffraction pattern is small (ie, the slope around zero overlay error is negligible). However, there is a large change in the diffraction pattern for the same given change in overlay error over a large overlay error. Similarly, if one wishes to evaluate other profile parameters, such as, for example, the sidewall angle or critical dimension of one of the populations, it is difficult to distinguish the two groups in order to evaluate their sidewall angle or critical dimension.

7A and 7B show exposed patterns in accordance with one embodiment of the present invention. FIG. 7A shows the main pattern in which a single pattern consisting of the first population A and the second population B exists. However, there is a small overlay error OV in the placement of the second population. 7B shows a target used in the first embodiment of the present invention. After the first target population was formed, a second target population was formed. The second target population has a bias Δ relative to the first target population. Thus, the placement deviation of the second target population relative to the first target population is equal to the overlay error OV plus the bias Δ. This introduced asymmetry means that it is much easier to determine the overlay error. The zeroth order diffraction pattern is detected and the deviation from the expected diffraction pattern is used to determine the overlay error. Alternatively, it is easier to distinguish the two groups and thus measure the characteristics of the two groups, such as the sidewall angle or the critical dimension of either group.

Although the embodiment described above has been described using two populations made using the LELE or LFLE process, this is equally applicable to the spacer method of double patterning. 8A and 8B illustrate a spacer method of double patterning according to an embodiment of the present invention. In FIG. 8A, a spacer 21 is used to create spaces between the resists 22, thus creating a regular pattern. FIG. 8B shows the situation where an overlay error OV exists between any parameter or adjacent features of either group when the spacer 21 is too small. Thus, the method of the embodiment described above can be similarly used to determine the overlay error. Known bias will be introduced by intentionally changing the size of the spacer and any property of the features being evaluated, as introduced by the size error of the spacer.

The bias can be any value, but must be smaller than the period of the pattern. For example, a bias of about 5-10 nm is preferred for a pattern having a period of about 16 nm.

For improved calculation of overlay error, there may be a plurality of targets (eg, each with their own target populations), each target having a different introduction bias.

Another embodiment of the present invention is shown in FIG. As can be seen, the second population B has a larger critical dimension than the first population A. Introducing this asymmetry again makes it easier to distinguish the two groups and to evaluate the characteristics of each group accordingly. 9 shows a second population with a larger critical dimension, but it may have an equally smaller critical dimension or alternatively have other characteristics such as a changed sidewall angle. Indeed, any characteristic that affects the zero-order diffraction pattern can be changed to produce this asymmetry.

Similar to the first embodiment, there may be a plurality of targets, each having a different critical dimension of the second target population.

10 illustrates a target population in which there are introduced bias and critical dimensions of the changed second population in accordance with one embodiment of the present invention. This in turn will make it easier to distinguish different groups and thus to measure the overlay error and characteristics of each group.

Another embodiment of the present invention is shown in FIG. 11, which shows another target population. As can be seen, the third line of the second group has all disappeared. Again, this introduces asymmetry which makes it easy to distinguish between the two groups.

As described above, this embodiment relates to asymmetric introduction into the target population. While specific examples of asymmetry, such as variations in lines, biases, and critical dimensions, which have disappeared above have been described, any method of introducing asymmetry would be appropriate. Still other examples of asymmetry between two populations may be a second population at different heights from the first population. Alternatively, different materials may be used for different populations. In addition, the present invention is not limited to the use of only two populations, and may be equally applied even when three or more populations exist.

Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, Display (LCD), thin-film magnetic heads, and the like. Those skilled in the art will recognize that any use of the terms "wafer" or "die" herein may be considered as synonymous with the more general terms "substrate" or "target portion", respectively, in connection with this alternative application I will understand. The substrate referred to herein can be processed before and after exposure, for example in a track (typically a tool that applies a resist layer to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where applicable, the description herein may be applied to such substrate processing tools and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

While specific reference may have been made above to the use of embodiments of the invention in connection with optical lithography, it is to be understood that the invention may be used in other applications, for example imprint lithography, and is not limited to optical lithography, I will understand. In imprint lithography, topography in a patterning device defines a pattern created on a substrate. The topography of the patterning device can be pressed into the resist layer supplied to the substrate on which the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is moved from the resist leaving a pattern therein after the resist is cured.

The terms "radiation" and "beam" as used herein refer to particle beams, such as ion beams or electron beams, as well as wavelengths (eg, 365, 355, 248, 193, 157 or 126 nm, or the like). All types of electromagnetic radiation, including ultraviolet (UV) radiation, and extreme ultraviolet (EUV) radiation (eg, having a wavelength within the range of 5-20 nm).

The term "lens ", as the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the present invention relates to a computer program comprising one or more sequences of machine-readable instructions for implementing a method as disclosed above, or to a data storage medium on which such computer program is stored (e.g., semiconductor memory, magnetic Or an optical disc).

conclusion

It is to be understood that the Detailed Description section of the invention, rather than the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may illustrate more than one, but do not describe all exemplary embodiments of the invention contemplated by the inventor (s), and do not in any way limit the invention and the appended claims. Do not.

In the above, embodiments of the present invention have been described with the aid of functional storing blocks illustrating the implementation of specified functions and their relationships. In this specification, the boundaries of these functional storage blocks have been arbitrarily defined for convenience of description. Alternate boundaries can be defined as long as the specified functions and their relationships are properly performed.

The foregoing description of specific embodiments is directed to the application of knowledge in the art to facilitate modification and / or adaptation of these specific embodiments without undue experimentation without departing from the general concept of the invention for various applications. The general nature of the invention will be revealed. Therefore, such applications and modifications are intended to be within the meaning and scope of equivalents of the described embodiments, based on the teachings and guidance presented herein. As used herein, the phraseology or terminology is for the purpose of description and not of limitation, and those skilled in the art should understand that the terminology or phraseology herein is to be interpreted in the light of teaching and guidance.

The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims (30)

In a method of determining characteristics of features on a substrate:
Forming a first population of a first target and a second population of a first target on a single layer of the substrate, wherein the first population of the first target is distinct from the first population of the second target;
Forming a second population of a first target and a second population of a second target on a single layer of the substrate, wherein the second population of the first target is distinct from the second population of the second target;
Detecting radiation reflected from the first target;
Calculating a first characteristic of a first population or a second population of the first target using the radiation reflected from the first target;
Detecting radiation reflected from the second target;
Calculating a second characteristic of the first population or the second population of the second target using the radiation reflected from the second target;
The first population of the first target has a first asymmetry with respect to the second population of the first target, the first population of the second target has a second asymmetry with respect to the second population of the second target,
The first asymmetry comprises a gap difference between features of the first and second populations of the first target, wherein the second asymmetry is a threshold dimension difference of the features of the first and second populations of the second target. Characteristic determination method comprising a. delete The method of claim 1,
And wherein the second asymmetry further comprises a gap difference between features of the first and second populations of the second target. The method of claim 1,
Wherein the first characteristic is an interval between a first population and a second population of the first target, and the second characteristic is an interval between the first and second populations of a second target. The method of claim 1,
And wherein the first asymmetry further comprises a difference in critical dimensions of features of the first and second populations of the first target. The method of claim 1,
The first asymmetry further comprises removing the n th feature of the first or second population of the first target,
The second asymmetry includes removing the n th feature of the first or second population of the second target,
and n is a finite number greater than one. The method of claim 1,
Wherein the first characteristic is a critical dimension of a feature of the first or second population of the first target and the second characteristic is a critical dimension of a feature of the first or second population of the second target. . The method of claim 1,
Wherein the first characteristic is a placement error of a second population of the first target, and the second characteristic is a placement error of a second population of the second target. The method of claim 1,
Wherein the first characteristic is a sidewall angle of a first population or a second population of the first target, and the second characteristic is a sidewall angle of a first population or a second population of the second target. The method of claim 1,
The first asymmetry includes that features of the second population of the first target differ in height, width, size, and ratio from features of the first population of the first target, wherein the second asymmetry is the first of the second target. And wherein the features of the second population differ in height, width, size, and ratio from the features of the first population of the second target. The method of claim 1,
Forming the first population of the first target and the first population of the second target includes exposing the substrate and processing the substrate, the second population of the first target and the second target Forming a second population of the substrates comprises subjecting the substrate to a second exposure and subjecting the substrate to a second treatment. The method of claim 1,
Forming the first population of the first target and the first population of the second target includes exposing the substrate and freezing the substrate, the second population and the second population of the first target. Forming a second population of targets includes subjecting the substrate to a second exposure and subjecting a second freezing. The method of claim 1,
Forming the first population of the first target and the second population of the first target and the forming the second population of the first target and the second population of the second target occur simultaneously. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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