JP2009288005A - Inspection method and apparatus, lithography apparatus, lithography processing cell, and device manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scatterometer measuring method and apparatus that performs measurement using widely spaced wavelengths or wavelength ranges. <P>SOLUTION: The scatterometer has a radiation source that emits radiation with different first and second wavelength ranges. In order to perform color correction according to need in accordance with which wavelength range is used, a variable optical element is provided. Accordingly, the single scatterometer can perform measurement using widely spaced wavelengths. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an inspection method that can be used, for example, for manufacturing a device by a lithography technique, and to a device manufacturing method that uses a lithography technique, and more particularly to a scatterometer measurement method.

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 such cases, a patterning device, alternatively referred to as a mask or reticle, can 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 (eg comprising part of, one, or several dies) on a substrate (eg a silicon wafer). The pattern is usually transferred by imaging onto a 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. A conventional lithographic apparatus scans a substrate in parallel or anti-parallel to a predetermined direction ("scan" direction) and a so-called stepper that irradiates each target portion by exposing the entire pattern to the target portion at once. However, each target portion is irradiated by scanning the pattern with a radiation beam in a predetermined direction ("scan" direction),
A so-called scanner. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0003] To monitor a lithographic process, one of the substrates that is usually patterned
One or more parameters are measured, such as an overlay error between successive layers formed in or on the substrate. There are a variety of techniques for measuring the microscopic structures formed in a lithographic process, including using scanning electron microscopes and various specialized tools. One form of professional inspection tool is a scatterometer that directs a beam of radiation to a target on the surface of a substrate and measures one or more properties of the scattered or reflected beam. By comparing one or more properties of the beam before and after reflection or scattering by the substrate, one or more 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 types of scatterometer are known. A spectroscopic scatterometer directs a broadband radiation beam to a substrate and measures the spectrum of the scattered radiation (intensity as a function of wavelength) in a specific narrow angular range. An angle-resolved scatterometer measures the intensity of scattered radiation as a function of angle. An ellipsometer measures the polarization state. Angle-resolved scatterometers and ellipsometers can use monochromatic beams, polychromatic beams (ie, beams with multiple components of different wavelengths), or broadband beams.

[0004] To use a broadband beam or a polychromatic beam, the optical system of the scatterometer needs to be achromatic. Techniques for achromating an optical system that includes refractive optical elements are well known, but become more complex and difficult as the number or range of wavelengths to be addressed increases. For example, an optical system using a mirror based on Schwarzschild optics can be made more easily achromatic, but the pupil plane is obscured, especially for scatterometers and ellipsometers with high NA optics. It is inappropriate.

[0005] It would be desirable to provide a scatterometer measurement method and apparatus that can measure, for example, using widely spaced wavelengths or wavelength ranges.

[0006] According to an aspect of the present invention, an inspection apparatus for determining a value related to a parameter of a target pattern printed on a substrate by a lithographic process used to manufacture a device layer on the substrate, comprising:
A radiation source that selectively emits a first radiation beam having a first wavelength in a first wavelength range, or a second radiation beam having a second wavelength in a second wavelength range different from the first wavelength range;
An optical system for directing a selected one of the first or second radiation beams to a target pattern and projecting the radiation re-directed by the target pattern onto a detector to obtain a scatterometry spectrum;
A variable optical element that selectively performs color correction of the optical system according to whether the radiation source emits the first radiation beam or the second radiation beam;
An apparatus comprising:

[0007] According to an aspect of the present invention, there is provided an inspection method for determining a value related to a parameter of a target pattern printed on a substrate by a lithographic process used to produce a device layer on the substrate, comprising:
The radiation source is controlled to selectively emit a first radiation beam having a first wavelength in the first wavelength range or a second radiation beam having a second wavelength in a second wavelength range different from the first wavelength range. ,
Using an optical system to direct a selected one of the first or second radiation beams to a target pattern, projecting the radiation re-directed by the target pattern onto a detector to obtain a scatterometry spectrum;
A method is provided that includes adjusting the variable optical element to selectively perform color correction of the optical system according to whether the first or second radiation beam is emitted from the radiation source.

[0008] According to an aspect of the invention, an inspection apparatus for determining a value related to a parameter of a target pattern printed on a substrate by a lithographic process used to produce a device layer on the substrate, comprising:
A first radiation beam having a first wavelength in the first wavelength range or a second radiation beam having a second wavelength in a second wavelength range different from the first wavelength range is guided to the target pattern and re-directed by the target pattern An optical system for projecting the emitted radiation onto a detector to obtain a scatterometry spectrum, comprising an objective lens having a pupil plane and collecting radiation redirected by a pattern, and an image of the pupil plane on the detector An optical system comprising an imaging optical system for projecting;
A variable optical element that selectively performs color correction of the optical system according to whether the first or second radiation beam is guided by the optical system;
An apparatus comprising:

[0009] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings. Corresponding reference characters indicate corresponding parts in the drawings.

[0016] FIG. 1a schematically depicts a lithographic apparatus. This device

[0017] an illumination system (illuminator) IL configured to condition a radiation beam B (eg UV radiation or DUV radiation);

[0018]-a support structure (eg, a mask table) configured to support the patterning device (eg, mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to certain parameters MT,

[0019] a substrate table (eg, a wafer table) configured to hold a substrate (eg, resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate according to certain parameters WT,

[0020] a projection system (eg, a refractive projection lens system) configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (eg, including one or more dies) of the substrate W ) PS.

[0021] The illumination system includes various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, etc. optical components, or any combination thereof, for directing, shaping or controlling radiation. You may go out.

[0022] The support structure supports, ie bears the weight of, the patterning device. The mask support structure holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and the like, for example, whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure can be a frame or a table, for example, and can 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.”

[0023] As used herein, the term "patterning device" is used broadly to refer to any device that can be used to pattern a cross-section of a radiation beam so as to generate a pattern on a target portion of a substrate. Should be interpreted. It should be noted here 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 shift features or so-called assist features. In general, the pattern imparted to the radiation beam corresponds to a special functional layer in a device being created in the target portion, such as an integrated circuit.

[0024] The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCDs
There is a panel. Masks are well known in lithography, and include mask types such as binary masks, alternating phase shift masks, attenuated phase shift masks, and various hybrid mask types. . As an example of a programmable mirror array, a matrix array of small mirrors is used, each of which can be individually tilted to reflect the incoming radiation beam in a different direction. The tilted mirror imparts a pattern to the radiation beam reflected by the mirror matrix.

[0025] As used herein, the term "projection system" refers to, for example, refractive optics systems, reflective optics, as appropriate to other factors such as the exposure radiation used or the use of immersion liquid or vacuum. It should be construed broadly to cover any type of projection system, including systems, catadioptric optical systems, magneto-optical systems, electromagnetic optical systems 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”.

The apparatus shown here is of a transmissive type (eg using a transmissive mask).
Alternatively, the device may be of a reflective type (eg using a programmable mirror array of the type mentioned above or using a reflective mask).

[0027] The lithographic apparatus may include two (dual stage) or more substrate tables (
And / or two or more mask tables). In such “multi-stage” machines, additional tables are used in parallel or one or more tables are used for exposure while one or more tables are used for preliminary processes can do.

[0028] The lithographic apparatus may be of a type wherein at least a portion of the substrate is covered with a liquid having a relatively high refractive index, such as water, so as to fill a space between the projection system and the substrate. An immersion liquid may be used in 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 projection systems. As used herein, the term “immersion” does not mean that a structure, such as a substrate, must be submerged in liquid, but rather that there is liquid between the projection system and the substrate during exposure. is there.

[0029] Referring to FIG. 1a, the illuminator IL receives a radiation beam from a radiation source SO.
The radiation source and the lithographic apparatus may be separate components, for example when the radiation source is an excimer laser. In such a case, the radiation source is not considered to form part of the lithographic apparatus, and the radiation beam is emitted from the radiation source SO with the aid of a beam delivery system BD, for example equipped with suitable guiding mirrors and / or beam expanders. Passed to the illuminator IL. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The radiation source SO and the illuminator IL are
If necessary, it can be called a radiation system together with a beam delivery system BD.

The illuminator IL may include an adjuster AD that adjusts the angular intensity distribution of the radiation beam. Typically, the outer and / or inner radius range (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution at the pupil plane of the illuminator can be adjusted. The illuminator IL may include other various components such as an integrator IN and a capacitor CO. Alternatively, the radiation beam may be adjusted using an illuminator so that desired uniformity and intensity distribution can be obtained across the cross section.

[0031] 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. The radiation beam B passes through the patterning device MA and passes through a projection system PS that focuses the beam onto a target portion C of the substrate W. With the help of the second positioner PW and the position sensor IF (eg interferometer device, linear encoder or capacitive sensor), the substrate table WT can be moved precisely to position various target portions C, for example in the path of the radiation beam B . Similarly, for the path of the radiation beam B using a first positioner PM and another position sensor (not explicitly shown in FIG. 1a), eg after mechanical retrieval from a mask library or during a scan Thus, the patterning device MA can be accurately positioned. In general, the movement of the support structure MT can be realized using a long stroke module (coarse positioning) and a short stroke module (fine positioning) that form part of the first positioner PM. Similarly, the substrate table W
The movement of T can be realized with the aid of a long stroke module and a short stroke module forming part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the support structure MT may be connected to a short stroke actuator only or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. The substrate alignment mark as shown occupies a dedicated target position, but may be arranged in a space between target portions (referred to as a scribe lane alignment mark). Similarly, in situations in which a plurality of dies are provided on the patterning device MA, patterning device alignment marks may be placed between the dies.

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

[0033] In step mode, the support structure 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 one time (ie one stationary exposure). ). The substrate table WT is then moved in the X direction and / or Y direction so that another target portion C can be exposed. In the step mode, the size of the target portion C on which an image is formed in one still exposure is limited by the maximum size of the exposure field.

[0034] 2. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (ie, one dynamic exposure). The speed and direction of the substrate table WT relative to the support structure MT can be determined by the enlargement (reduction) and image reversal characteristics of the projection system PS. In the scan mode, the maximum size of the exposure field limits the width of the target portion (in the non-scan direction) in one dynamic exposure, and the length of the scan operation determines the height of the target portion (in the scan direction). .

[0035] 3. In another mode, the support structure MT is held essentially stationary while holding the programmable patterning device, and projects the pattern imparted to the radiation beam onto the target portion C while moving or scanning the substrate table WT. In this mode, a pulsed radiation source is typically used to update the programmable patterning device as needed each time the substrate table WT is moved or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.

[0036] Combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

[0037] As shown in FIG. 1b, the lithographic apparatus LA forms part of a lithographic cell LC, sometimes referred to as a lithocell or cluster, that performs one or more pre-exposure and post-exposure processes on the substrate. It also includes a device to perform. Conventionally, these include one or more spin coaters SC for depositing resist layers, one or more developers DE for developing exposed resists, one or chill plates CH and one or more bake plates B.
K is included. The substrate handler, that is, the robot RO picks up the substrate from the input / output ports I / O1 and I / O2, moves it between the different process apparatuses, and sends it to the loading bay LB of the lithographic apparatus. These devices are often collectively referred to as tracks and are under the control of the track control unit TCU, which is itself controlled by the supervisory control system SCS, which also controls the lithographic apparatus via the lithography control unit LACU. . Thus, various devices can be operated to maximize throughput and processing efficiency.

[0038] In order to accurately and consistently expose a substrate to be exposed by a lithographic apparatus, the exposed substrate is inspected to measure properties such as subsequent interlayer overlay errors, line thickness, critical dimension (CD), etc. Is desirable. If an error is detected, the subsequent exposure of the substrate can be adjusted, especially if the inspection can be performed immediately and quickly enough to still expose other substrates in the same batch. Also, an already exposed substrate can be removed (to improve yield) and reworked or discarded, thereby avoiding performing exposure on substrates that are known to be defective. If only some target portions of the substrate are defective, further exposure can be performed with only good target portions. There is also the possibility of adapting the setting of subsequent process steps to compensate for the error. For example, the trim etch step time can be adjusted to compensate for CD variations from substrate to substrate caused by the lithography process steps.

[0039] Using an inspection device to determine one or more characteristics of a substrate, particularly in different layers or different layers of the same substrate, how one or more characteristics differ from layer to layer and from substrate to substrate Ask. The inspection apparatus can be integrated into the lithographic apparatus LA or the lithocell LC or can be a stand-alone device. In order to enable the quickest measurement, it is desirable that the inspection apparatus measures the characteristics of the exposed resist layer immediately after exposure. However, the latent image of the resist has a very low contrast, and the refractive index of the resist portion exposed by radiation and the unexposed portion must be very small. It does not have enough sensitivity to measure. Thus, the measurement can be performed after a post-exposure bake step (PEB), which is the first step performed on a customarily exposed substrate and improves the contrast between the exposed and unexposed portions of the resist. At this stage, the image in the resist can be said to be semi-potential. It is also possible to measure the developed resist image at points where the exposed or unexposed portions of the resist have been removed, or after a pattern transfer step such as etching. The latter possibility limits the possibility of reworking a defective substrate, but can still provide useful information, for example for process control purposes.

[0040] FIG. 2 shows a scatterometer SM1 according to an embodiment of the present invention. This is the substrate W
A broadband (white light) radiation projector 2 for projecting radiation onto. The reflected radiation is passed to the spectroscopic detector 4 which measures a spectrum 10 of specularly reflected radiation (ie a measure of intensity as a function of wavelength). From this data, the structure or contour giving rise to the detected spectrum is reconstructed by the processing unit PU, for example by rigorous coupled wave analysis and nonlinear regression or by comparison with a library of simulated spectra as shown at the bottom of FIG. can do. In general, to reconstruct, the overall form of the structure is known, some parameters are assumed from the knowledge of the process that created the structure, and only some parameters of the structure are derived from the scatterometer measurement data. It is left to ask. Such a scatterometer can be configured as a normal incidence scatterometer or an oblique incidence scatterometer.

[0041] According to an embodiment of the present invention, the radiation source 2 is configured to selectively output radiation in at least two different wavelength ranges, such as the UV range (less than 300 nm) and the near infrared range (700-800 nm). It can be controlled. The radiation source 2 can include a first radiation source, such as a deuterium lamp or a xenon lamp, to emit UV radiation. Thus, the first wavelength range that can be output by the radiation source can be in the range of about 200 nm to about 300 nm. The radiation source 2 can include a second radiation source, such as a quartz tungsten halogen source or a laser, to emit near infrared radiation. The second wavelength range that can be output by the radiation source can range from about 700 nm to about 800 nm. In both the first and second radiation sources, one or more filters can be provided to limit the emitted wavelength range to the desired range. The first and second radiation sources are selectively energized to output radiation in the first and second wavelength ranges. Alternatively, both radiation sources can be energized simultaneously and individual shutters can be opened or closed or beam redirecting elements can be moved to select the output from the desired radiation source. If the different wavelength ranges to be used are close enough, one adjustable radiation source may be used. To be selectable from more than two wavelength ranges, more than two selectable radiation sources and / or adjustable radiation sources can be provided.

[0042] Radiation in the UV range is useful for CD measurements, and the obtainable CD value decreases with improved lithographic techniques, so shorter wavelengths are required for accurate measurement. Near infrared range radiation is useful for measuring the overlay of polysilicon or polysilicon-like layers. Other wavelength ranges may be particularly useful for other measurements. By providing a radiation source that can selectively emit two or more different ranges, different measurements such as CD and overlay can be performed with one scatterometer. This reduces the number of scatterometers installed in the factory and improves throughput. This is because multiple measurements can be performed on a substrate without having to move the substrate between scatterometers.

[0043] The optical system (not shown) of the scatterometer SM1 needs to be adapted to the various wavelength ranges to be used. Therefore, the compliant optical element AE1 is provided at the appropriate position in the scatterometer optical system and performs the necessary corrections under the control of the control unit CU when a different wavelength range is selected. The variable element AE1 may take a variety of different forms. For example, a controllable deformable mirror, a controllable deformable lens element,
A movable lens element, a plurality of lens elements having adjustable relative positions and / or interchangeable lens elements can be provided.

[0044] Another scatterometer SM2 that can be used in embodiments of the present invention is illustrated in FIG. In this device, the radiation emitted by the radiation source 2 is transmitted to the lens system 12.
Is focused through the interference filter 13 and the polarizer 17 and the partially reflective surface 16
And is focused on the substrate W via the objective lens 15 of the microscope, which preferably has a high numerical aperture (NA) of at least 0.9 or at least 0.95. The immersion scatterometer may have a lens with a numerical aperture greater than one. The reflected radiation then passes through the partially reflective surface 16 and enters the detector 18 to detect the scattered spectrum. The detector can be placed on the back-projected pupil plane 11, which is at the focal length of the lens system 15, but the pupil plane is re-imaged onto the detector 18 with auxiliary optics (not shown). be able to. The pupil plane is a plane in which the radial position of the radiation defines the incident angle and the angular position defines the azimuth angle of the radiation. The detector is preferably a two-dimensional detector so that a two-dimensional angular scatter spectrum of the substrate target (ie, a measure of intensity as a function of scattering angle) can be measured. The detector 18 may be an array of CCD or CMOS sensors, for example, and may have an integration time of 40 milliseconds per frame, for example.

[0045] A reference beam is often used, for example, to measure the intensity of incident radiation.
To do so, when the radiation beam is incident on the partially reflective surface 16, a portion of it is transmitted through the surface as a reference beam toward the reference mirror. The reference beam is then projected onto a different part of the same detector 18.

[0046] One or more interference filters 13 can be used to select the wavelength of interest, for example in the range of 405 to 790 nm, or even lower ranges such as 200 to 300 nm. The interference filter may be adjustable rather than comprising a set of different filters. A diffraction grating can also be used in place of or in addition to one or more interference filters.

[0047] The detector 18 measures the intensity of scattered light at one wavelength (or narrow wavelength range), measures the intensity separately at a plurality of wavelengths, or measures the intensity integrated over a range of wavelengths. be able to. Furthermore, the detector can measure separately the intensity of TM (transverse magnetic) polarized radiation and the intensity of TE (transverse electric) polarized radiation and / or the phase difference between TM polarized radiation and TE polarized radiation.

[0048] It is possible to use a broadband radiation source 2 (ie a light source whose frequency or wavelength of radiation and thus a wide range of colors), which gives a large etendue and allows for the mixing of multiple wavelengths. Each of the plurality of broadband wavelengths has a bandwidth of λδ and an interval of at least 2λδ (
That is, it is preferable to have twice the wavelength. Some radiation “sources” may be different portions of the extended radiation source that are split using, for example, fiber bundles. By this method, the angle-resolved scattering spectrum can be measured in parallel at a plurality of wavelengths. A three-dimensional spectrum (wavelength and two different angles) can be measured, which contains more information than a two-dimensional spectrum. This allows more information to be measured, which improves the robustness of the measurement process. This is described in further detail in US Patent Application Publication No. US 2006-0066855A, which is hereby incorporated by reference in its entirety.

[0049] Like the embodiment described with respect to FIG. 2, the radiation source 2 selectively emits radiation having a wavelength (or set of wavelengths) in the first wavelength range or the second wavelength range by means of the control unit CU. Can be controlled. According to the selected range, the variable element AE2 is controlled to perform the necessary compensation of the optical system. The radiation source 2 and variable element AE2 may take the same form as the corresponding parts of the embodiment described with respect to FIG. In connection with the selection of the wavelength range or set output by the radiation source 2, one or more filters 13 are exchanged or adjusted.

[0050] As shown, the variable element AE2 is provided in the measurement branch of the scatterometer SM2, ie between the sample and the detector 18, but may also be provided in the illumination branch, ie between the radiation source 2 and the sample. . More than one variable element can be provided, for example one for each branch. The variable element AE2 can also be provided in the high NA objective lens 15.

[0051] A scatterometer SM3 according to a further embodiment of the invention is illustrated in FIG. In this embodiment, two light sources 31, 32 provide a beam of radiation having orthogonal polarization states such as p and s, which are collected by lenses 33 and 34 to form a virtual light source, which is a polarizing beam splitter. 35. As described above, each radiation source is controllable to emit radiation in the first or second wavelength range. The aperture plate 20 is provided with one or more openings to shape the illumination beam, for example conventional illumination,
It can be annular and / or multipolar illumination. A selection mechanism 23 such as a motor can be used to select one of the plurality of openings in the plate.

The relay optical systems 36 and 37 include a non-polarizing beam splitter 39 and an objective lens 40.
Then, a measurement spot is projected onto the substrate W held on the substrate table WT. The mirror can be deformed under the control of a control unit CU (not shown) in order to perform the necessary color correction in synchronization with the selected wavelength range output by the radiation sources 31, 32. The objective lens 40 has a high NA, for example greater than 0.90 or 0.95, and thus forms a pupil plane PP inside which is detected by a lens 45 and a detector 45 such as a CCD array or other form of camera. Re-imaged. A movable knife edge 44 is provided for light collection.

[0053] The non-polarizing beam splitter 39 directs a portion of the incident beam to the reference mirror 48 via the mirror 46 and the lens 47, from which the beam returns and is directed to the detector 45 to form a reference spot; If there are fluctuations in the intensity of the light source, all the effects can be removed.

[0054] A scatterometer SM4 according to a further embodiment of the invention is illustrated in FIG. This scatterometer is largely the same as the scatterometer SM3 described above,
Therefore, description of common parts is omitted.

[0055] Instead of the deformable mirror 38, the scatterometer SM4 has a simple folding mirror 38a, which is partially silvered for coupling with a light collection system (not shown) in illumination. Can do. In order to perform the necessary optical system correction according to the selected wavelength range, two (or more) replaceable objective lenses 40a, 40b are provided together with the actuator 40c to perform the objective lens exchange. One of the interchangeable objective lenses is optimized for each wavelength range (or set) that can be output by the radiation sources 31, 32. As an alternative, the variable element may be provided in the high NA objective lens 40.

[0056] In any of the scatterometers described above, the target on the substrate W can be a diffraction grating printed so that a bar is formed with a solid line of resist after development. The bars can be etched into the substrate alternately. The target pattern is selected to be sensitive to the parameters of interest, such as focus, dose, overlay, chromatic aberration, etc. of the lithographic projection apparatus, so that relevant parameter variations will manifest as printed target variations . For example, the target pattern may be sensitive to chromatic aberrations of a lithographic projection apparatus, in particular the projection system PL, and the symmetry of illumination and the presence of such aberrations will manifest as variations in the printed target. Accordingly, the target pattern is reconstructed using the scatterometer data of the printed target pattern. From knowledge of the printing step and / or other scatterometer measurement processes, target pattern parameters such as line width and shape can be input into the reconstruction process and executed in the processing unit.

[0057] From the data obtained from the scatterometer (referred to as the spectrum), to determine the value of the target problem parameter, such as the critical dimension (CD),
There are two basic methods. Iterative modeling and library search. Iterative modeling techniques use a theoretical model of the target structure to calculate the spectrum acquired from the target as a function of the parameter in question. Starting from the initial value or seed value, the expected spectrum is calculated and compared with the measured spectrum so that the estimate of the parameter value can be improved. This process is repeated for a number of iterations until the expected spectrum matches the measured spectrum within the desired error limits, at which point the actual value of the parameter is used to obtain the expected spectrum. It is assumed that the expected value of the parameter is equal within the desired accuracy.

[0058] In the library search technique, models that relate spectra to parameter values are used again to build a library of expected spectra, and the measured spectra are compared to library items to find the closest match. The number of items in the library is determined by the range of parameter values expected to be possible, which depends on how accurately the parameter values can be predicted in advance and the accuracy of the desired measurement values.

[0059] Another technique that can be used in a scatterometer is Principal Component Analysis.
Analysis PCA). In this technique, the value of the parameter of interest is varied to print a test pattern or calibration pattern matrix. Each spectrum can be represented by acquiring and analyzing a spectrum for each test pattern to derive a set of principal components (basis functions) and thus multiplying the principal components by a set of coefficients. Thus, a function for associating the coefficient with the parameter value can be derived from the known parameter value of the test pattern. The spectrum from the measurement target is decomposed into a coefficient to be multiplied by the main component, and the parameter value is obtained using the coefficient value.

[0060] In order to ensure the accuracy of the scatterometer measurement, the optical system needs to be free of aberrations within the desired range. This requires that the aberrations of the optical system can be measured. A conventional method for measuring aberrations in optical systems such as those used in scatterometers is interferometry. However, interferometry techniques require additional hardware, are time consuming, and are difficult to perform on the device in use. Therefore, periodic calibration and diagnostic monitoring cannot be performed without leaving the scatterometer out of use for a significant period of time.

[0061] Although the text specifically refers to the use of a lithographic apparatus in the manufacture of ICs, it will be appreciated that the lithographic apparatus described herein has other uses. For example,
These include integrated optical devices, magnetic domain memory guidance and detection patterns, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like. In light of these alternative applications, use of the terms “wafer” or “die” herein are considered synonymous with the more general terms “substrate” or “target portion”, respectively. Those skilled in the art will recognize that this may be the case. The substrates described herein are processed before or after exposure, for example, with a track (usually a tool that applies a layer of resist to the substrate and develops the exposed resist), metrology tools, and / or inspection tools. be able to. Where appropriate, the disclosure herein may be applied to these and other substrate processing tools. In addition, the substrate can be processed multiple times, for example to produce a multi-layer IC, so the term substrate as used herein can also refer to a substrate that already contains multiple processed layers.

[0062] While the above specifically refers to the use of embodiments of the present invention in the context of optical lithography, the present invention can also be used in other applications such as imprint lithography,
It is understood that the situation is not limited to optical lithography, if allowed. In imprint lithography, the pattern generated on the substrate is defined by the microstructure of the patterning device. The microstructure of the patterning device is pressed against a layer of resist supplied to the substrate, after which the resist is cured by electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved away from the resist, leaving a pattern after the resist is cured.

[0063] As used herein, the terms "radiation" and "beam" include not only particle beams such as ion beams or electron beams, but also ultraviolet (UV) radiation (eg, about 365 nm, 355 nm, 248 nm, 193 nm). Having wavelengths at or near 157 nm or 126 nm) and extreme ultraviolet (EUV) radiation (eg 5 nm to 20 n)
covers all types of electromagnetic radiation, including (with wavelengths in the range of m).

[0064] The term "lens" refers to any of various types of optical components, or combinations thereof, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components, as the situation allows.

[0065] 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 provides a computer program that includes one or more sequences of machine-readable instructions that describe a method as disclosed above, or a data storage medium (eg, semiconductor memory, etc.) that stores such a computer program. Magnetic or optical disk).

[0066] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

[0010] FIG. 1 shows a lithographic apparatus. [0011] FIG. 1 shows a lithographic cell or cluster. [0012] FIG. 1 is a diagram illustrating a first scatterometer according to an embodiment of the present invention. [0013] FIG. 4 is a diagram illustrating a second scatterometer according to an embodiment of the present invention. [0014] FIG. 5 shows a third scatterometer according to an embodiment of the present invention. [0015] FIG. 5 shows a fourth scatterometer according to an embodiment of the present invention.

Claims (20)

An inspection apparatus for determining values related to parameters of a target pattern printed on a substrate by a lithographic process used to produce a device layer on the substrate,
A radiation source that selectively emits a first radiation beam having a first wavelength in a first wavelength range or a second radiation beam having a second wavelength in a second wavelength range different from the first wavelength range;
An optical system for directing the selected one of the first or second radiation beams to the target pattern and projecting the radiation re-directed by the target pattern onto a detector to obtain a scatterometry spectrum;
A variable optical element that selectively performs color correction of the optical system in accordance with whether the first or second radiation beam is emitted from the radiation source;
A device comprising:   The apparatus of claim 1, wherein the first wavelength range is 5 to 300 nm.   The apparatus of claim 1, wherein the second wavelength range is 400 to 800 nm. The apparatus of claim 1, wherein the first radiation beam has a plurality of components each having an individual wavelength in the first wavelength range. The apparatus of claim 1, wherein the second radiation beam has a plurality of components each having an individual wavelength in the second wavelength range. The apparatus of claim 1, wherein the first radiation beam is a broadband beam having a wavelength range in the first wavelength range. The apparatus of claim 1, wherein the second radiation beam is a broadband beam having a wavelength range in the second wavelength range.   The apparatus of claim 1, wherein the variable optical element comprises a deformable mirror.   The apparatus of claim 1, wherein the variable optical element comprises a variable refractive lens element. The apparatus of claim 1, wherein the variable optical element comprises a refractive lens element and an actuator that adjusts the position and / or orientation of the refractive lens element. The apparatus of claim 1, wherein the variable optical element comprises a pair of refractive lens elements and an actuator that adjusts a relative position of the pair of variable lens elements. The apparatus of claim 1, wherein the variable optical element comprises a plurality of replaceable optical elements and an actuator that selectively places one of the replaceable optical elements in the optical system. The optical element projects an illumination branch that directs the selected one of the first or second radiation beams to the target pattern, and projects the radiation re-directed by the target pattern onto a detector for scatterometry. The apparatus of claim 1, further comprising: a detection branch configured to acquire a spectrum, wherein the variable optical element is provided in the illumination branch. The optical system projects an illumination branch configured to direct the selected one of the first or second radiation beams to the target pattern, and radiation redirected by the target pattern onto a detector. And a detection branch for obtaining a scatterometry spectrum, wherein the variable optical element is provided in the detection branch. The apparatus of claim 1, wherein the optical system comprises an objective lens system and the variable optical element is provided in the objective lens system. The apparatus of claim 1, wherein the variable optical element comprises a plurality of objective lens units that are selectively positionable within the optical system. An illumination optical system for illuminating the pattern;
A projection optical system that projects an image of the pattern onto a substrate;
An inspection apparatus for determining values related to parameters of a target pattern printed on the substrate by a lithographic process used to produce a device layer on the substrate;
The device comprises:
Directing a first radiation beam having a first wavelength in a first wavelength range or a second radiation beam having a second wavelength in a second wavelength range different from the first wavelength range to the target pattern;
An optical system that projects radiation redirected by the target pattern onto a detector to obtain a scatterometry spectrum;
A variable optical element that selectively performs color correction of the optical system according to whether the first radiation beam or the second radiation beam is guided by the optical system;
Lithographic apparatus. A coater that coats the substrate with a radiation sensitive layer;
A lithographic apparatus for exposing an image to the radiation-sensitive layer of a substrate coated with a coater;
A developer for developing an image exposed by the lithographic apparatus;
An inspection apparatus for determining values relating to parameters of a target pattern printed on the substrate by a lithographic process used to produce a device layer on the substrate;
The device comprises:
Radiation configured to selectively emit a first radiation beam having a first wavelength in a first wavelength range, or a second radiation beam having a second wavelength in a second wavelength range different from the first wavelength range. The source,
Directing the selected one of the first or second radiation beams to the target pattern, projecting the radiation re-directed by the target pattern onto a detector;
An optical system for acquiring a scatterometry spectrum;
A variable optical element that selectively performs color correction of the optical system according to whether it is the first or second radiation beam emitted by the radiation source;
Lithography cell. An inspection method for determining values related to parameters of a target pattern printed on a substrate by a lithographic process used to produce a device layer on the substrate, comprising:
Control the radiation source to selectively emit a first radiation beam having a first wavelength in the first wavelength range or a second radiation beam having a second wavelength in a second wavelength range different from the first wavelength range. And
An optical system is used to direct the selected one of the first or second radiation beams onto the target pattern, project the radiation re-directed by the target pattern onto a detector, and a scatterometry spectrum Get
Adjusting a variable optical element to selectively perform color correction of the optical system according to whether the first or second radiation beam is emitted from the radiation source. An inspection apparatus for determining values related to parameters of a target pattern printed on a substrate by a lithographic process used to produce a device layer on the substrate,
Directing a first radiation beam having a first wavelength in a first wavelength range, or a second radiation beam having a second wavelength in a second wavelength range different from the first wavelength range, to the target pattern;
An optical system that projects radiation redirected by the target pattern onto a detector to obtain a scatterometry spectrum, the objective having a pupil plane and collecting the radiation redirected by the pattern; An optical system comprising: an imaging optical system that projects an image of the pupil plane onto the detector;
A variable optical element that selectively performs color correction of the optical system according to whether the first radiation beam or the second radiation beam is guided by the optical system.

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