JP5221912B2 - Lithographic element contamination measurement method and system - Google Patents

Description

  The present invention relates generally to lithography, and more particularly to lithography of semiconductor processes. In particular, the invention relates to a method for measuring contamination of lithographic elements. The invention also relates to a system for measuring contamination of lithographic elements.

  Optical lithographs today use wavelengths of 248 nm or 193 nm. Integrated circuit (IC) fabrication down to 45 nm node or 32 nm node is possible using 193 nm immersion lithography. However, for printing at sub-32 nm half-pitch nodes, this wavelength is probably not satisfactory due to theoretical limitations unless double patterning is used. Instead of using a wavelength of 193 nm, a more advanced technique called extreme ultraviolet lithography (EUV lithography) has been introduced, which uses a wavelength of 10 nm to 14 nm, a typical value of 13.5 nm. This technique has previously been known as soft X-ray lithography using wavelengths in the range of 2 nm to 50 nm in detail.

  In optical lithographs at several wavelengths in the deep ultraviolet (DUV) range, electromagnetic radiation is transmitted through most materials, such as glass used in conventional lenses and masks.

  On the other hand, at short wavelengths, such as extreme ultraviolet lithography and soft x-ray lithography, electromagnetic radiation is absorbed by most materials, such as glass used in conventional lenses and masks. Therefore, completely different tools are required to perform EUV lithography compared to conventional optical lithography. Instead of using lenses, such imaging systems currently rely entirely on reflective optics, and are composed of reflective optical elements called cattoptric elements, such as mirrors, for example. These reflective optical elements, eg mirrors, are preferably coated with a multilayer structure designed to have a high reflectivity (reach 70%) at a wavelength of 13.5 nm. Furthermore, since air also absorbs EUV light, a vacuum environment is required.

US Patent Publication No. 2003/0011763 US Patent Publication No. 2005/0083515

Although EUV lithographs are believed to be applicable using wavelengths below 32 nm, many problems still need to be overcome to reach mature technology. As shown in the document “KR Dean et al in Proc. Of SPIE 6153E, p.1-9 (2006)”, one of these problems is contamination of the optical system by chemical components, and “contamination”. This component is usually a gas component derived from resist outgassing. This resist degassing occurs due to EUV irradiation of the EUV resist. In the region where the emitted light is incident on the EUV optical system, contamination components that degas during exposure may contaminate the EUV optical system, resulting in both the reflectance of the reticle and the reflectance of the imaging optical system. Decrease. As a result, the lifetime of the EUV optical system is significantly reduced by contamination. According to the International Semiconductor Technology Roadmap (ITRS), the 2-minute degassing rate of the organic material under the lens should be less than 5e13 (5 × 10 ¹³ ) mol / cm ² · sec.

In order to reduce the resist degassing rate, a weighing tool capable of measuring the resist degassing amount for a certain resist is required. One possibility for screening for resist degassing is also described in the document "KR Dean et al in Proc. Of SPIE 6153E, p.1-9 (2006)". A degas chamber is built in the synchrotron beam line. A Si ₃ N ₄ reference plate with the wafer is placed in the chamber and exposed to EUV radiation. This reference plate is then analyzed using an electron spectrometer for chemical analysis (ESCA) to find evidence of accumulated contamination. Contaminants are collected in thermal desorption (TD) tubes. Contaminants in these TD tubes are analyzed by a gas chromatography / mass spectrometer (GC / MS) for chemical analysis.

  US Patent Publication No. 2003/0011763 describes a projection exposure apparatus that is useful for projection exposure of a pattern defined on a mask onto a substrate in the manufacture of semiconductor devices. This apparatus includes a cleaning device for cleaning the optical member. Prior to the pattern transfer, by removing the contaminants generated by the previous pattern transfer by the cleaning operation, the contamination of the substrate facing surface of the optical member can be reduced during the pattern transfer. In an embodiment of U.S. Patent Publication No. 2003/0011763, a numerical value regarding a contamination level determined based on a difference between a predetermined reflectance of an optical member and an actually determined reflectance is from an allowable range. When it comes off, a cleaning operation is performed. The predetermined reflectance is determined immediately after the device is manufactured.

  US Patent Publication No. 2005/0083515 describes a method for evaluating the reflection uniformity of an optical component having an EUV reflective surface used in EUV lithography. This method is used to determine the reflectance loss of the substrate derived from the coating and the substrate. According to the embodiment of US 2005/0083515, the reflectance map of a test piece is compared to a separately characterized reference piece of the same design.

  With special interest in in-situ measurements of contamination, other techniques and systems are still needed to analyze resist degassing.

  The object of the present invention is to provide a good method and system for characterizing contamination of lithographic elements.

  An advantage of embodiments of the present invention is that a contaminated lithographic element, such as a contaminated lithographic optical element, is directly contaminated, for example a reflective optical element such as a mirror or a contaminated reticle, to directly measure the parameters of the contaminated lithographic element. It is to provide a method and system for measuring the reflectivity and transmissivity of lithographic elements. According to some embodiments of the present invention, a method for measuring contamination of a lithographic element compares a parameter of the contaminated lithographic element with a reference parameter associated with the lithographic element in an uncontaminated state. Thus, direct measurement may be to measure parameters of the lithographic element itself.

  According to some embodiments of the present invention, parameters such as reflectance are measured in the processing chamber, meaning that no ex-situ reflectance measurements are required. An advantage of such an embodiment according to the invention is that the parameters of the processing chamber, for example the irradiation light source used, can be taken into account directly. According to some embodiments of the invention, parameters such as reflectivity are measured in the processing chamber of the metering system. According to some embodiments of the invention, parameters such as reflectivity are measured in a processing chamber of a lithographic processing system. This method avoids extensive manipulation of lithographic elements and reduces the risk of measurement fluctuations due to manipulation of contaminated lithographic elements. This method avoids the use of fragile reference optical elements such as reference mirrors. This method allows in-situ measurements on the relevant optical parameters of the contaminated element, reducing the need for expensive and time consuming test setup and recalibration procedures.

  An advantage of embodiments of the present invention is to provide a system for performing the method according to the present invention. According to some embodiments of the invention, the system may be a metering system or a lithographic processing system.

  The above objective is accomplished by a method and system according to the present invention.

According to a first aspect of the invention, the method measures contamination of a lithographic element, the method comprising providing the first lithographic element in a processing chamber;
Providing a second lithographic element in the processing chamber;
A portion of the first lithographic element is covered, a reference area that is a covered portion of the first lithographic element is provided in the first lithographic element, and a test area that is an uncovered portion of the first lithographic element is provided in the first lithographic element. Steps,
Supplying contaminants into the processing chamber;
Directing the exposure beam toward the test area of the first lithographic element and the second lithographic element such that the at least one lithographic element is contaminated by contaminants;
Measuring a contamination level of at least one contaminated lithographic element within the processing chamber. The method preferably includes the step of removing the coated portion of the first lithographic element to provide an uncoated reference region. Measuring the contamination level preferably comprises optically measuring the contamination level.

  An advantage of the present invention is that optical measurements can be used on the same object and performed with the same parameters / conditions on that object, providing more accurate parameters and providing a more accurate inspection of contamination levels it can. By using a test area and a reference area on the same object, a more accurate correlation can be created.

  An advantage of embodiments of the present invention is that contamination can be measured within the processing system. An advantage of embodiments of the present invention is that contamination can be measured using the same light beam as the exposure beam and the optical measurement beam. An advantage of embodiments of the present invention is that contamination is measured by determining the optical properties of only the contaminated component, and no separate elements are required.

  According to some embodiments of the present invention, the step of coating a portion of the first lithographic element comprises installing a shield that covers a portion of the first lithographic element, and at least a portion of the shield and the first lithographic element. Between the two, a hard contact, that is, a direct contact may be included.

  According to another embodiment of the present invention, the step of covering a portion of the first lithographic element comprises installing a shield that covers a portion of the first lithographic element, and at least a portion of the shield and the first lithographic element. In between, it may include installing a soft contact.

  Measuring the contamination level optically may include measuring optical parameters at the test area and the reference area.

  According to some embodiments of the present invention, the step of covering a portion of the first lithographic element may include installing a shield that shields at least a portion of the first lithographic element.

  According to some embodiments of the present invention, a resist may be provided in the processing chamber, and contaminants may be supplied into the processing chamber by degassing the resist. The first lithographic element may be a lithographic optical element.

  According to some embodiments of the invention, the first lithographic element may be a mirror or a lens.

  According to some embodiments of the present invention, the method may further include removing contaminants from the processing chamber prior to measuring the contamination level of at least one contaminated lithographic element in the processing chamber. Good. Removing the contaminant may include removing the source of contamination. Further, removing contaminants may include reducing residual contamination present in the gas state in the chamber. Removing the contaminants may include removing a lithographic element with a resist layer on the top surface and / or removing degassing released by the resist layer from the processing chamber. Removing the contaminant may include removing a contaminant gas previously introduced into the chamber. Such removal may be accomplished, for example, by purging the chamber with a purge gas or pumping the chamber to a predetermined level.

  Optically measuring the contamination level may include measuring optical parameters for the test area and the uncovered reference area.

  According to some embodiments of the invention, the method may further include the step of cleaning the processing chamber prior to measuring the contamination level of at least one contaminated lithographic element in the processing chamber. .

  According to some embodiments of the invention, the at least one contaminated lithographic element may be a first lithographic element.

  According to some embodiments of the invention, measuring the contamination level of at least one contaminated lithographic element in the processing chamber may include measuring the contamination level of the first lithographic element.

According to some embodiments of the present invention, measuring the contamination level of the first lithographic element in the processing chamber comprises:
Measuring a value for the parameter in the uncovered reference region of the first lithographic element, which is a reference value for the parameter;
Measuring a value for the parameter in the test area of the first lithographic element, which is a test value for the parameter;
The step of determining a difference between the reference value and the test value, for example by calculation, may be included.

  According to some embodiments of the present invention, measuring the reference value of the parameter may include directing the exposure beam to the sensor via the reference region of the first lithographic element. Alternatively, separate beams may be used to expose lithographic elements and to measure optically.

  According to some embodiments of the present invention, measuring the parameter test value may include directing the exposure beam to the sensor via the test area of the first lithographic element.

  According to some embodiments of the invention, the second lithographic element may include a contaminant. According to some embodiments of the present invention, the second lithographic element may comprise a resist containing contaminants.

  According to some embodiments of the invention, the second lithographic element may comprise a lithographic optical element. If possible, the second lithographic element is a mask.

  According to some embodiments of the present invention, supplying the contaminant into the processing chamber may include supplying a gaseous compound into the processing chamber.

  According to some embodiments of the invention, at least the second lithographic element is contaminated by contaminants in the step of directing the exposure beam to the second lithographic element via the test area of the first lithographic element. May be. According to some embodiments of the invention, measuring the contamination level of at least one lithographic element in the processing chamber may include measuring the contamination level of at least a second lithographic element in the processing chamber. .

According to some embodiments of the invention, measuring the contamination level of at least a second lithographic element in the processing chamber comprises:
By directing the exposure beam through the reference area of the first lithographic element towards the second lithographic element and further towards the sensor, the second element test value for the parameter in the test area of the second lithographic element A measuring step may be included.

  According to some embodiments of the present invention, the step of measuring the second element test value directs the exposure beam through the test area of the first lithographic element to the second lithographic element and further toward the sensor. The method further includes:

  According to some embodiments of the invention, the first lithographic element may be a mirror. According to some embodiments of the invention, the measurement parameter may be the reflectivity of the first lithographic element. The sensor may be a reflectance sensor.

  According to some embodiments of the invention, the first lithographic element may be a lens. According to some embodiments of the invention, the measurement parameter may be the transmittance of the first lithographic element. The sensor may be a transmittance sensor.

  According to some embodiments of the invention, the sensor may include a diode.

  According to some embodiments of the present invention, the test area may include a plurality of test zones. The reference area may include a plurality of reference zones.

According to a first aspect of the present invention, there is provided a system for measuring contamination of a lithographic element, the system comprising:
A processing chamber;
An entrance for introducing pollutants,
A first for supplying a first energy beam into the processing chamber adapted to cause contamination of the at least one lithographic element by exposing the at least one lithographic element directly or indirectly in the presence of the contaminant. Energy sources,
Means for coating at least a portion of the first lithographic element to provide a reference area for the first lithographic element, wherein the reference area is not contaminated when the first lithographic element is exposed to the first energy beam. Covering means to
A sensor for measuring contamination.

  The system may comprise means for introducing a first lithographic element into the processing chamber and means for introducing a second lithographic element into the processing chamber. According to an embodiment of the present invention, the first energy beam may measure a parameter of at least one lithographic element.

  According to an embodiment of the invention, the system may comprise a second energy source for supplying a second energy beam into the processing chamber, wherein the second energy beam is a parameter of at least one lithographic element. You may make it measure.

  According to an embodiment of the present invention, the processing chamber may be a vacuum processing chamber.

  According to an embodiment of the present invention, the first energy source may emit electromagnetic radiation in the extreme ultraviolet range.

  According to an embodiment of the present invention, the sensor may be a reflectance sensor or a transmittance sensor. The sensor may be an optical sensor. According to embodiments of the present invention, the sensor may include a diode.

The invention also relates to a method for measuring contamination of a lithographic element in a processing chamber from a lithographic system, the processing chamber comprising at least a first lithographic element and a second lithographic element, the method comprising:
Supplying contaminants into the processing chamber;
Exposing the test area of the first lithographic element and the second lithographic element so that the at least one lithographic element is contaminated by contaminants and not exposing a portion of the at least one lithographic element; Obtaining a reference region for a contaminated lithographic element;
Optically measuring the contamination level of the at least one contaminated lithographic element in the processing chamber by measuring optical parameters for the test region and the reference region of the at least one contaminated lithographic element.

  Other features and characteristics of the method and corresponding system may be as presented in other methods and systems described for the present invention.

  Compared to the prior art, different advantages of the proposed embodiment will be obtained. In the prior art, contamination measurement of lithographic elements, in particular lithographic optics, collects various contaminating chemical components and these chemical components can be combined with a mass spectrometer or the document “KR Dean et al in Proc. Of SPIE 6153E, p.1-9 (2006) "by analysis using similar analytical techniques. Contaminants are collected in thermal desorption (TD) tubes. Contaminants in these TD tubes are analyzed by a gas chromatography / mass spectrometer (GC / MS) for chemical analysis. This technique of recovering contaminating chemical components is not repeatable because the sample is destroyed. The results are therefore subject to relatively large statistical fluctuations.

  Understanding the impact of these contaminating components on the optical lithographic elements results in additional uncertainty and variability as it requires more complex calculations and simulations.

  In various embodiments of the present invention, this deficiency in chemical analysis techniques can directly measure the parameters of the contaminated lithographic optical element itself, e.g., measure the reflectance or transmittance of a contaminated mirror. This has been overcome at least in part by measuring the reflectance or transmittance of the contaminated reticle. Parameters such as reflectance are measured in the processing chamber, which means that no ex-situ reflectance measurements are required.

  In general, reflectance measurements using, for example, a standard reflectometer are performed by observing the light source and the sample simultaneously to obtain a value representing the sample reflection relative to the reference. This approach would require a reference mirror to split the incident beam and would require the installation of an additional second detector. This requirement is extremely demanding for measuring contamination of lithographic elements. A long term reflectance change of about 1% is expected, which means that a reproducibility of 0.1% or better is targeted. The stability of the reference mirror as used in general reflectance measurements can be a significant problem. It becomes contaminated over time and produces artifacts even at fairly low rates. Similarly, the need for two detectors will cause certain problems. Avoiding artifacts requires complex recalibration procedures, along with gold standards for mirrors and detectors. With embodiments of the present invention, some or all of these problems and deficiencies for standard reflectance measurements will be overcome. Only one detector is used and the reference mirror is integrated as a reference region in the sample itself, for example a mirror or a reticle.

  In addition, for standard reflectometry, the use of a reference mirror is more complicated in that mirrors with different compositions and stacks need to be inspected. This means that different samples require different reference mirrors and different recalibration procedures. These deficiencies can be overcome by embodiments of the present invention that allow different reference areas and different test areas to be placed on a single sample (eg, a mirror).

  Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and features of other dependent claims as appropriate, not just those explicitly stated in the claims.

  Although there has been constant improvement, change and evolution of devices in this field, this concept is considered to represent a substantially new and new improvement, including developments from previous practices, and is more efficient. To provide a stable and reliable device of this kind.

  The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. This description is for purposes of illustration only and is not intended to limit the scope of the invention. The following reference drawings refer to the attached drawings.

  In the different drawings, the same reference signs refer to the same or analogous elements.

  The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements are exaggerated and not drawn on scale for illustrative purposes. The dimensions and relative dimensions do not correspond to the actual embodiment of the present invention.

  Further, the terms first, second, third, etc. in the detailed description and in the claims are used to distinguish similar elements and are not necessarily for describing the order in time or space. The terms so used are interchangeable under appropriate circumstances, and it should be understood that the embodiments of the invention described herein can operate in a different order than those described and illustrated herein. It is.

  Further, the terminology, top, over, etc. in the detailed description and in the claims are used for explanation purposes and are not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances, and it should be understood that the embodiments of the invention described herein can operate in a different order than those described and illustrated herein. It is.

  It should be noted that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. . Should be construed as specifying the presence of the described feature, integer, step or component, as referenced, but one or more other features, integers, steps or components, or groups of these It does not exclude existence or addition. The scope of the expression “a device including means A and means B” should not be limited to a device consisting only of the components A and B. In the context of the present invention, it means that only the relevant components of the device are A and B.

  Reference throughout this specification to “one embodiment” or “an embodiment” includes within the at least one embodiment of the invention the particular feature, structure or characteristic described in connection with the embodiment. Means that. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment, but may be. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as will be apparent to those skilled in the art from this disclosure in one or more embodiments.

  Similarly, in describing example embodiments of the present invention, various features of the present invention are sometimes described in a single implementation for the purpose of streamlining disclosure and support in understanding one or more of the various inventive aspects. Grouped together in form, drawing or description. This method of disclosure, however, should not be interpreted as reflecting an intention that the claimed invention requires more features than are recited in each claim. Rather, as the following claims reflect, inventive aspects exist less than all the features of a single, previously disclosed embodiment. Thus, the claims following the detailed description are incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

  Further, some embodiments described herein may or may not include some other features included in other embodiments. Combinations of features of different embodiments are within the scope of the present invention, as will be understood by those skilled in the art, and are meant to form different embodiments. For example, in the following claims, any of the claimed embodiments can be used in any combination.

  Furthermore, some embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or other means of performing the function. A processor with the instructions necessary to implement such a method or method element forms the means for performing the method or method element. Furthermore, the elements of the apparatus embodiments described herein are examples of means for performing the functions performed by the elements for the purpose of carrying out the invention.

  In the description provided here, many specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure the understanding of this description.

  The following terms are provided only to assist in understanding the invention.

  The term “outgassing” should be understood as the release of gaseous contamination into the clean room and / or processing chamber by equipment, equipment or tools or components thereof. This term is also referred to as offgassing.

  Resist degassing means that the resist releases gas or gas for a certain period in lithographic processing.

  “Shielding” means that an area of a lithographic element is prevented from being irradiated by radiation and is not contaminated when exposed to contaminants and irradiation. Many techniques may be provided for shielding.

  Hard contact should be understood as providing a contact between the shield or cover and the lithographic element. There is substantially “no gap” between the shield or cover and the lithographic element, ie the shield or cover and the lithographic element are in direct contact with each other. The contacts may be airtight and gaseous contamination cannot reach the contact area of the lithographic element, but embodiments of the invention are not so limited.

  Soft contacts should be understood to provide shielding by a shield on the lithographic element. Such shielding is preferably substantially free of radiation that can reach the shielded area of the lithographic element or is substantially reduced compared to when direct radiation is possible. That is. For this purpose, a shield may be provided close to the lithographic element. This is, for example, a distance of less than 1 nm. Such a reduction may be 60%, more preferably 80%, even more preferably 95%, even more preferably 99%. The shield may create a shadow so that the shield is positioned separately from the lithographic element and incident radiation does not pass through the shield. This shield casts a shadow over an area of the lithographic element to prevent direct exposure.

The term “extreme ultraviolet radiation” includes electromagnetic radiation in the wavelength range of 31 nm to 1 nm.
The term “X-ray radiation” typically includes electromagnetic radiation in the wavelength range of 10 nm to 0.01 nm.
The term “deep ultraviolet radiation” is electromagnetic radiation typically in the wavelength range of 300 nm to 7 nm.

  The invention will now be described by a detailed description of several embodiments of the invention. It will be apparent that other embodiments of the invention may be constructed according to the knowledge of those skilled in the art without departing from the true spirit or technical teaching of the invention, and the invention is intended only by the terms of the appended claims. Limited.

  Embodiments of the present invention are suitable for lithographic systems and methods using electromagnetic radiation with wavelengths having the same order of magnitude, or wavelengths smaller than the thickness of the reticle feature. This typically includes extreme ultraviolet (EUV) radiation, deep ultraviolet radiation, x-ray radiation. Note that the present invention is not limited to these, and slight variations in the wavelength range may occur.

  Embodiments of the present invention may typically relate to a lithographic metering system. A lithographic weighing system is typically used for characterization and / or optimization of parameters in a lithographic processing or lithographic processing system. Lithographic processing is typically performed in a lithographic processing system often referred to as a lithographic exposure tool. Embodiments of the invention may also relate to a lithographic processing system.

  As used herein, the term “contaminant” is used to define an object, material or substance that induces contamination. The contaminant is formed by or associated with, for example, but not limited to, a solid or gaseous contaminant, such as from a photoresist. The contaminant may also be present in gaseous form in any other suitable manner. Contamination may be introduced by the presence of foreign species, for example, water vapor and hydrocarbons in a vacuum and / or intentionally through, for example, resist degassing, eg, hydrocarbons only, or a leak valve. Introduced components and the like. Contamination appears as a decrease in reflectivity due to adsorbed species, which is also referred to as reflection loss or adsorption contamination. When the photoresist is exposed, resist degassing occurs. Resist degassing is caused by photoproducts that degas from the resist during exposure. These degassing components become condensed on the optical elements of the exposure tool, degrading the optical system of the lithographic system. Component contamination may occur in the optical components and other parts of the chamber during exposure or during periods other than exposure. Nonetheless, when exposed, the contamination on the irradiated surface is significantly higher, and in some embodiments of the invention the primary focus is on the irradiated surface contamination.

  Typically, advanced photolithographs use chemically amplified photoresist. These resists contain a photoacid generator (PAG) that degassed with EUV radiation under vacuum. In general, a resist consists of a polymer backbone, a solvent, a protecting group, a quencher, and suitable additives. The most common degassed products are derived from decomposition products from protecting groups and PAGs. In EUV lithography, contamination is also caused by hydrocarbons from degassed components from the resist polymer itself during EUV radiation in a vacuum environment. Possible resist degassing components include, but are not limited to, isobutane, isobutene, acetone, tert-butylbenzene, methylstyrene, hydronaphthalene, benzene, and the like, depending on the resist used. Other contaminants may be, for example, compounds (inorganic or organic) added into the lithographic system via a gas inlet, which can induce contamination in the lithographic optics, for example from clean room air, For example, when mounting filtered particles (usually not molecular contaminants), eg clean room materials such as floor covers, filters, sealing materials, piping, wafer boxes, wafer carriers, adhesives, pellicles From the tape used, monomers, oligomers such as caprolactam from nylon vessels, silicone and siloxane derivatives from sealing materials, processing aids and stabilizers such as additives, plasticizers such as dioctyl phthalate, dibutyl phthalate Benzoquino such as cross-linking agent, diacetylbenzene, antioxidant , Organic phosphorus compounds, such as fire retardants, tributyl Fe - DOO and the like.

  Lithographic systems (eg, EUV tools, immersion tools, etc.) are typically installed in a clean room environment. From this clean room environment, for example, by introducing a wafer into the lithographic system, organic compounds present in the clean room may enter the lithographic system and form a source of contamination.

  The term “lithographic optical element” as referred to herein is used to define an optical element, which is typically used in a lithographic processing system. Different optical elements are used depending on the wavelength of electromagnetic radiation used in the lithographic process. For example, in an EUV lithographic system, a wavelength of 13.5 nm is used in vacuum, so the optical element needs to be reflective at the present time. EUV lithographic exposure involves at least four optical components: a collector that captures as much radiation as possible from the illumination source, an illumination system that uniformly illuminates the field of use on the mask, and a transfer to the wafer substrate An imaging optical system for reducing the structure of the mask itself including the power pattern and the structure from the mask to the wafer is required.

  In EUV lithography, all these optical systems are currently composed of reflective elements such as mirrors, for example. The mask is also often referred to as a reticle and is an optical element, in particular a reflecting mirror. The reticle is typically a type of mask used in a stepper or scanner, typically using a reduction optical system, and the image on the reticle is magnified. A mask / reticle is a plate with a pattern of transparent and opaque regions used to create a pattern on a wafer.

  In EUV lithography, the mask / reticle starts as a complete EUV mirror and the pattern is formed on the top surface as an absorbing layer or by making certain portions non-reflective by etching into the mirror. EUV mirrors (eg used in illumination systems) start from a curved and flat surface at the atomic level, on which a special multilayer coating is formed. The coating is tuned to provide peak reflectivity for only one wavelength of EUV light (ie 13.5 nm). Alternatively, the lithographic optical element may be a lens, such as used in deep ultraviolet (DUV) lithographs. DUV lithography uses longer wavelengths (eg, 248 nm, 193 nm, 157 nm) compared to EUV lithography (ie, 13.5 nm). At these wavelengths, light can be transmitted by conventional lenses.

  In a first embodiment, the present invention relates to a method for measuring contamination of a lithographic element. Exemplary steps performed in a method according to an embodiment of the present invention are illustrated in the flow diagram of one embodiment of a method (100) for measuring contamination in FIG. A method for measuring contamination of a lithographic element includes providing a first lithographic element in the processing chamber (101), providing a second lithographic element in the processing chamber (102), and one of the first lithographic elements. Covering a portion (103), providing a reference region that is a covering portion of the first lithographic element on the first lithographic element, and providing a test region that is an uncovered portion of the first lithographic element on the first lithographic element; Supplying a contaminant into the processing chamber (104) and redirecting the exposure beam through the test area of the first lithographic element to the second lithographic element so that at least one lithographic element is contaminated by the contaminant; A step (105) of at least one contaminated lithographic element in the processing chamber; And a step (106) for measuring the dyeing level.

  The exposure beam may be directed first to the second lithographic element and then to the first lithographic element. In other words, the order of irradiating the lithographic elements may be different. The latter is particularly the case when measuring contamination with a weighing tool, but it can also be applied to actual lithographic processing tools.

  These steps will be described in more detail with reference to FIGS. 2 (a), (b), and (c). In a first step of the method for measuring contamination in a lithographic system, a first lithographic element is introduced into the processing chamber (101). The processing chamber may be part of a lithographic metering system or part of a lithographic processing system. The supplying step may mean a situation where there is no need to actively supply, for example, a system in which the first lithographic element is already present, for example a measuring instrument for carrying out the method of the invention is installed. It may be a lithographic system that is also used for efficient lithographic processing. Thus, the installation of the first lithographic element may be performed during system installation or in a preceding operation. In other words, the aggressive supply step is optional.

  The first lithographic element (201) may be introduced directly from the atmospheric environment in the lithographic system (not shown in FIG. 2 (a)). However, in the case of a lithographic system under vacuum, such as an EUV lithographic system, after the introduction of the first lithographic element (201), the lithographic system needs to be pumped to a vacuum level. Therefore, it is preferable to use a load-lock chamber to introduce the first lithographic element (201). The load lock chamber is an inlet system from the atmosphere (202a) to the vacuum (202b) to facilitate the entry and exit of objects into the vacuum system. For example, in an EUV lithographic system, the EUV tool internal environment is under vacuum (202b). By using the load lock chamber (202), the lithographic system can be maintained under vacuum when the first lithographic element is introduced from the atmospheric environment (202a) into the EUV tool.

Initially, the first lithographic element (201) is transferred from the atmospheric environment (202a) into the load lock chamber (202). The load lock chamber is then pumped to a pressure at the lithographic system, eg, a pressure on the order of about 10 ⁻⁷ mbar. The first lithographic element (201) is then transferred from the loadlock chamber (202) into a lithographic system that is under the same or at least as high pressure (202b) as the loadlock.

  In the lithographic system (202b), the first lithographic element may be positioned on a movable stage so as to be movable into the lithographic system. The first lithographic element may be movable as required in the step of comparing contamination levels as described below.

  The first lithographic element may be a lithographic optical element. The first lithographic element may be a mirror or a lens. In EUV lithography, a reflective mirror is typically used. The reflecting mirror can be manufactured with a coating made of alternating films of molybdenum (Mo) and silicon (Si). By increasing the number of alternating layers, the reflectivity of the mirror can be increased. A conventional lens is used in the DUV lithography. The lens will transmit electromagnetic radiation and the mirror will reflect electromagnetic radiation. When mirrors are used, the reflectivity of electromagnetic radiation is generally measurable to characterize the mirror. When a lens is used, the transmittance of electromagnetic radiation is generally measurable to characterize the lens. The contamination of the mirror or the lens can be measured by measuring the reflectance and transmittance, respectively.

  In the next step of the method for measuring contamination of a lithographic element, a second lithographic element (203) is introduced (102) into the processing chamber. Since the second lithographic element is already present in the processing chamber and may have been introduced, for example, during installation or during a previous operation, active introduction is optional. A load lock chamber may be used to introduce the second lithographic element (203) (not shown in FIG. 2 (a)). Alternatively, the second lithographic element (203) may be introduced directly from the atmospheric environment into the lithographic system (as in FIG. 2 (a)). For example, in the case of a lithographic system under vacuum, such as an EUV lithographic system, after the introduction of the second lithographic element (203), the lithographic system needs to be pumped again to a vacuum level.

  In another step of the method for measuring contamination of a lithographic element, a portion of the first lithographic element is covered (103) to provide a reference area (201b). Such coating can be performed before or after the introduction of the contaminant, preferably before the introduction of the contaminant. The coating must be done before the exposure of the lithographic element. The covering portion of the first lithographic element is covered when at least a part of the first lithographic element (201) or the reference region (201b) is covered and does not change, and is referred to when comparing different regions of the first lithographic element. Means to function as.

  The coated part is referred to as the reference area (201b) and remains the same before and after exposure of the exposure beam to electromagnetic radiation and / or contaminants. Neither contaminant nor exposure radiation interacts with the coated portion or reference region 201b. The uncovered portion is referred to as the test area (201a) and the first lithographic element will be exposed to electromagnetic radiation and / or contaminants. As a result, contaminants or exposure radiation will interact with the uncovered portion or test area 201a.

  Covering a portion of the first lithographic element may include shielding the first lithographic element from contaminants using a shield. Shielding the first lithographic element from contaminants may include providing a hard contact between the shield and a portion of the first lithographic element. Alternatively, shielding the first lithographic element from contaminants may include providing a soft contact between the shield and a portion of the first lithographic element. Alternatively, the shield may be positioned so as to avoid radiation falling on the reference area, i.e., shadowing the reference area of the first lithographic element.

  FIG. 2 (b) shows the step of shielding at least a portion (201b) of the first lithographic element to prevent the reference region (201b) from being contaminated. This shield (204) moves, for example, in front of the reference area (201b) and uses a shutter that makes a hard or soft contact between the shield and the first lithographic element, or the shutter or shield is the first. This may be done mechanically by creating a shadow in the reference area of the lithographic element to prevent radiation from entering the shielding area of the first lithographic element.

  Depending on the contaminant, the spacing may vary. The spacing preferably prevents contaminants from reaching and interacting with the shielding portion of the lithographic element. The shield may be positioned so that contaminants cannot interact with the shielding portion of the lithographic element. The shield may be any material that has the property of preventing contaminants from interacting with the underlying portion of the lithographic element.

  Preferably, one reference area is defined above the first lithographic element. Alternatively, the reference region may include a plurality of reference zones, for example two or three reference zones. Preferably, one uncovered part forming the test area is defined on the first lithographic element. Alternatively, other embodiments of the invention may include a plurality of uncoated portions that form a plurality of test zones. More test areas can be defined, for example, two reference zones can be defined, and three reference zones can be defined.

  By defining more test areas on the first lithographic element, different characteristics of the first lithographic element can be analyzed in a single measurement. For example, but not limited to, if the first lithographic element is a mirror, two reference zones and two test zones can be defined on the mirror (FIG. 4). The mirror includes, for example, a first portion (401) including 40 Mo / Si layers having a specific cap layer on the upper surface and a second portion including 40 Mo / Si layers not including the cap layer on the upper surface. Part (401 *). In the first portion (401), one first zone (401b) of the reference region may be covered, and the second portion (test zone 401a) may be uncovered. In the second part (401 *) of the mirror, one first zone (which is the second reference zone 401b *) may be covered and the second part (which is the second test zone 401a *) may be uncovered. . The reference zones (401b, 401b *) may be simultaneously covered by the shield 404. Alternatively, a separate shield may be used to cover the reference zone.

  In the next step of the method for measuring contamination of lithographic elements, contaminants are supplied into the processing chamber of the lithographic system. The contaminant may be any component that allows contamination of the first and / or second lithographic elements. The contaminant is not limited to this, but may be an organic compound or any gaseous compound. The organic compound can be introduced directly into the processing chamber or indirectly into the processing chamber. Direct introduction of contaminants means introduction into the lithographic system via the inlet (310) (FIG. 3 (a)). These are, for example, gases such as carrier gas contaminated with the above organic compounds. Introducing a contaminant indirectly means introducing the contaminant using a second lithographic element.

  In certain embodiments of the invention, the second lithographic element includes a contaminant. The second lithographic element may include a resist. For example, if the second lithographic element (203) is a wafer, the wafer may be coated with a resist (203 ′) that contains contaminants, which typically forms a mask pattern on the wafer. Used in lithographs to define. It is known from the prior art that resists contain contaminants because resist degassing occurs as soon as the wafer (with resist on top) is exposed to vacuum and / or exposed to electromagnetic radiation. Yes.

  In the next step of the method for measuring contamination of a lithographic element, an exposure beam is directed to a second lithographic element via a test area of the first lithographic element, whereby at least one lithographic element is contaminated (105). Contaminated by.

  In one embodiment of the present invention, in the step of redirecting the exposure beam (205) to the second lithographic element via the test area of the first lithographic element, the first lithographic element is contaminated by a contaminant, thereby at least 1 One lithographic element is contaminated with contaminants. In this step, the first lithographic element is, for example, by electromagnetic radiation (205) from an EUV light source (207) or using any other wavelength that can be used in a lithographic setting (FIG. 2 (b)), Exposed.

  Beam exposure and interaction with contaminants will contaminate unshielded areas (including at least one test area (210a)) of the first lithographic element (201). The shielding area or at least one reference area (201b) of the first lithographic element remains uncontaminated. The first lithographic element may be a mirror (201) and the second lithographic element is a wafer (203) with resist (203 ') (as a contaminant) on the top surface.

  The EUV light source (207) emits EUV electromagnetic radiation (205) onto the mirror (201). The EUV light (205 ') is reflected from the mirror (201) to the wafer (203) provided with the resist (203') by the mirror positioned at the angle α. As soon as the wafer with resist on top is exposed to EUV light, resist degassing occurs (206). Components supplied by resist degassing can contaminate at least one test area (201a) of the mirror, but due to shielding from resist degassing positioned on the upper surface of at least one reference area, Does not contaminate at least one reference region (201b).

  Alternatively, DUV light may be used to expose the first lithographic element. In this case, the light is not reflected (like EUV light) but is transmitted. The mirror is positioned at an angle α, and the beam from the beam source reflects at this angle α and travels from the first lithographic element to the second lithographic element. This angle α is preferably 45 degrees, but may in principle range from about zero to about 90 degrees. A second lithographic element, such as a wafer, may be scanned during the contamination step to induce sufficient resist degassing.

  In a subsequent step of the method for measuring contamination of a lithographic element, contaminants, in particular the source of contamination, may be removed from the processing chamber and the processing chamber is cleaned. If the contamination rate is sufficiently low compared to the contamination measurement time and / or depends on the required measurement accuracy, this step may not be performed. Therefore, these steps are optional. Removing the pollutant means keeping away the source of contamination so that no further contamination occurs. For example, if the contaminant is a degassing component of the resist on the top surface of the wafer, the wafer with the resist on the top surface can be removed and no more exposure to electromagnetic radiation (FIG. 2 (c)). Alternatively, it can be removed from the chamber to avoid degassing under vacuum. If the resist is not further exposed to electromagnetic radiation, resist degassing will not occur.

  Processing chamber cleaning may be performed, for example, by outbaking to remove these gases or other contaminants present in the processing chamber. Outbaking is the heating of the vacuum equipment, particularly the workpieces contained within the vacuum chamber during operation, while maintaining the lowest possible operating pressure, removing adsorbed gas from the surfaces and cavities within the vacuum chamber. Other cleaning methods as known to those skilled in the art may be used. It will be apparent that in order to obtain contamination information for lithographic elements, such elements should not be cleaned prior to inspection of the contamination that is occurring.

  In a next step of the method of measuring lithographic element contamination, the contamination level of at least one contaminated lithographic element in the processing chamber is measured. In this step, various preferred embodiments are described. This step preferably includes stripping the coating, i.e. removing the coating of the reference region of the first lithographic element. The shielding of at least one reference area of the first lithographic element is removed. Removing the occlusion means removing at least one reference area protecting and covering or shadowing (FIG. 2 (c)). “Unshielding” may be performed mechanically, for example, using a shutter that moves away from at least one reference region (201b). After this step, which is performed after exposure, the first lithographic element is contaminated with at least one part (201b) that is unchanged compared to the part before exposure (201b) and part before the exposure (201a). At least one portion (at least one test area) (201a ′).

  In certain embodiments of the invention, the step of measuring the contamination level of at least one lithographic element in the processing chamber further measures the contamination level of the first lithographic element (106).

  Measuring the contamination level of the first lithographic element in the processing chamber includes measuring a value related to the parameter of the reference region of the first lithographic element, i.e. obtaining a reference value related to the parameter, and testing the first lithographic element. The method further includes measuring a value relating to the parameter of the region, ie obtaining a test value relating to the parameter, and determining a difference between the reference value and the test value, for example by calculation.

  The first lithographic element due to the difference, eg contamination due to contamination, by comparing at least the contamination level in the test area (related to the test value) and the contamination level in the reference area (related to the reference value) The relative loss of the parameter values is determined and calculated, for example.

  If the first lithographic element is a reflective element, such as a mirror, the reflectivity of the first lithographic element may vary depending on the amount of contamination by the contaminant. In EUV lithographic measurement, for example, the reflectivity of the mirror is preferably about 70%. Contamination causes the mirror reflectivity to degrade by a few percent (typically 1-2%) depending on the amount of contaminants and exposure due to the presence of components derived from resist degassing, for example. There is. As a result, the lifetime of optical elements (mirrors, masks, etc.) is reduced and this is a major concern in lithographs because these optics are extremely expensive. Considering that multiple mirrors are used in an EUV lithographic exposure tool, the total loss of reflectivity increases. The change in reflectance due to contamination is as low as possible, preferably 0.1% or 0. It is important to keep it below a few percent. To measure the (relative) change in reflectance of an object due to contamination, the reflectance from at least one test area of the object is compared to the reflectance from at least one reference area of the object. The parameter used to detect the contamination is shown as reflectance, which is compatible with the system under test and / or lithographic system, but for example surface diffusivity, specular reflection, total reflection, For example, the transmittance may be used when a lens is used.

  FIG. 2A illustrates one embodiment of the present invention for measuring contamination of a first lithographic optical element in-situ, ie, within a processing chamber. The measurement performed to detect contamination may be an optical measurement. After removing the shielding from at least one reference area (201b) of the first lithographic element, at least one (contamination) test area (201a ′) of the first lithographic element is exposed to an exposure beam, eg, a radiation source (207). Exposed to electromagnetic radiation from. The radiation source may be the same radiation source used to introduce lithographic processing or contamination, or used to make an optical measurement of contamination, for example, by deriving optical parameters from a contaminated lithographic element. May be a separate radiation source. Such a radiation source may provide electromagnetic radiation, such as extreme ultraviolet radiation, deep ultraviolet radiation, ultraviolet radiation, visible light, and the like. An exposure radiation beam, eg, a light beam, is reflected from the first lithographic element, and the reflected beam (205 ″) is for measuring the reflected radiation intensity of at least one test area (201a ′) of the first lithographic element. It enters the sensor 208. The contaminant does not affect the reflectivity of the first lithographic element because the contaminant is no longer exposed (contaminant is removed).

  In a subsequent step, the movable first lithographic element is moved (209) so that the exposure radiation beam from the light source exposes at least one reference region (201b) of the first lithographic element. Again, the radiation is reflected from the at least one reference region and is directed to a sensor that measures the reflected radiation intensity of the at least one reference region of the first lithographic element.

  FIG. 2A shows a typical reflectance curve that could be extracted. The difference Δ is the difference in reflected radiation intensity between at least one test area (201a ') of the first lithographic element and at least one reference area (201b) of the first lithographic element. If at least one test area (201a ') is contaminated, a decrease in reflectivity will be measured. It should be noted that using this in-situ measurement, only relative values of reflectivity can be obtained.

  To obtain the absolute value of reflectivity for at least one test region and at least one reference region, additional reflectivity measurements may be performed ex-situ, ie outside the processing chamber. These ex-situ reflectance measurements can be performed by any technique known to those skilled in the art, such as a reflectometer. The radiation source used during the contamination step is preferably the same as the radiation source used to analyze the lithographic elements. Alternatively, a separate radiation source may be used.

  Alternatively, if DUV radiation is used (instead of EUV radiation), the transmission difference can be measured between at least one test area and at least one reference area. After removing the shield from the at least one reference area of the first lithographic element, the radiation of the radiation source is used to analyze at least one (contamination) test area of the first lithographic element. The radiation source is preferably the same as the radiation source used to expose the first lithographic element, but the invention is not so limited. When using DUV radiation, the radiation will be transmitted through the first lithographic element, and the transmitted light beam is incident on a sensor for measuring the transmittance of at least one test area of the first lithographic element. become. The contaminant does not affect the transmittance of the first lithographic element because the contaminant is no longer exposed (contaminant is removed).

  In a subsequent step, the movable first lithographic element is moved so that the light beam from the light source exposes at least one reference region of the first lithographic element. Again, radiation is transmitted from the at least one reference region and directed to a sensor that measures the transmittance of the at least one reference region of the first lithographic element.

  If the optical parameters of at least one contaminated lithographic element are to be determined, this can be done with any suitable optical sensor suitable for detecting radiation from the illumination source used in the contamination measurement. The reflectivity may be measured using a reflectivity sensor, which may be a diode. Alternatively, the transmittance is measured using a transmittance sensor. This sensor may be a diode. The sensor for measuring the reflectivity may be a diode with EUV sensitivity or any other kind of EUV detector. Alternatively, if an electromagnetic radiation source having a wavelength in the DUV region is used, a diode having DUV sensitivity, or any other type of DUV detector may be used.

  In another embodiment of the invention describing a method for measuring contamination of a lithographic optical element, the second lithographic element is a reticle or mask. For example, the reticle can be supplied with several exposure levels (eg, at different locations), and only one test location is used, eg, on the mirror (which is the first lithographic element).

  Each step will be described in detail with reference to FIGS. 3A to 3C when the second lithographic element is a mask or a reticle and the contamination of the lithographic element is measured.

  In a first step of the method for measuring contamination of a second lithographic element, the second lithographic element is a mask or reticle and a movable first lithographic element (301) is introduced into the lithographic system.

  The first lithographic element (301) may be introduced directly from the atmospheric environment into the lithographic system (not shown in FIG. 3 (a)). However, in the case of a lithographic system under vacuum, for example an EUV lithographic system, after the introduction of the first lithographic element (301), the lithographic system needs to be pumped again to a vacuum level. Thus, a load lock chamber (302) may preferably be used to introduce the first lithographic element (301). The first lithographic element may be positioned on the movable stage so as to be movable within the lithographic system. Similar to the above, the first lithographic element may already be located in the system, for example, when the system is installed or during a previous operation.

  In the next step of the method for measuring contamination of the second lithographic element, the second lithographic element (303) is a reticle or mask and is introduced into the processing chamber. A load lock chamber (302) may be used to introduce the second lithographic element (303) (not shown in FIG. 3 (a)). Alternatively, the second lithographic element (303) may be introduced directly from the atmospheric environment into the lithographic system (as in FIG. 3 (a)). Similar to the above, the first lithographic element may already be located in the system, for example, when the system is installed or during a previous operation.

  In the next step of the method for measuring contamination of the second lithographic element, contaminants are generated or inserted in the lithographic system. The contaminant (306) may be any component that causes contamination of the first and / or second lithographic elements (indicated by an asterisk in FIG. 3 (b)). The contaminant is, for example, but not limited to, an organic compound. Organic compounds are introduced directly into the lithographic system. Direct introduction of contaminants (intentional contaminants) means introduction into the lithographic system via the entrance (310) (FIG. 3 (a)). This may be, for example, a gas such as a carrier gas contaminated with an organic compound as described above.

  In another step of the method of measuring contamination of the second lithographic element, the second lithographic element (303) is a mask or reticle, wherein at least one reference region is defined by a shield on the first lithographic element, and at least One test area is defined on the first lithographic element. Reference region (301b) means a portion or region of the first lithographic element, which remains unchanged during processing and can serve as a reference when measuring the contamination level of the second lithographic element. The reference area (301b) remains unchanged upon exposure to electromagnetic radiation and / or contaminants.

  Shielding or covering should preferably take place before adding contaminants. This can substantially reduce or eliminate contamination on the shielding area even when exposure is off. Nevertheless, shielding or coating should be performed between the introduction of the contaminant and the exposure of the optical element, as most contamination problems arise when surface contamination occurs during the exposure of these walls. Thus, once the mirror / mask is illuminated, it is preferred that a shield or coating be present.

  Contaminants and exposure light do not interact with the reference area. Test area (301a) means a part or area of the first lithographic element, which is exposed to light and / or contaminants. Contaminant or exposure light interacts with the test area. Preferably, one reference region is defined on the first lithographic element. Alternatively, the reference area may comprise one or more reference zones, for example two or three reference zones. Preferably, one test area is defined on the first lithographic element. Alternatively, the test area may comprise one or more test zones, for example two or three test zones.

  At least one reference region of the first lithographic element is shielded (FIG. 3 (b)) to prevent contamination of the at least one reference region (301b). Shielding means that the reference region (301b) is coated (304) and is not contaminated when exposed to contaminants, or at least not exposed to contaminants and exposure simultaneously.

  This shielding (304) may be done mechanically, for example by using a shutter that moves in front of the reference area (301b) and casts a shadow on the reference area on the first lithographic element. Another possibility for shielding at least one reference region of the first lithographic element is any way of creating a soft or hard contact between the shield and at least one reference region of the first lithographic element. Any shield may be used, such as creating a shadow, or providing a soft or hard contact between the shield and a first lithographic element, such as a mirror.

  In the next step of the method for measuring contamination of the second lithographic element, the second lithographic element (303) is a reticle or mask and the exposure beam (305, 305 ') passes through the test area of the first lithographic element. To the mask or reticle, thereby contaminating at least one lithographic element with contaminants. Due to the inserted contaminant (306), the second lithographic element, which is a mask or reticle, becomes contaminated (303 '). If possible, the test area of the first lithographic element, for example the mirror (301a '), is also contaminated. Due to exposure of radiation (305, 305 ') and interaction with contaminants, for example from other parts of the tool, the unshielded zone (at least one test area (301a) of the first lithographic element (301) ) And the second lithographic element (303 ′) become contaminated.

  The shielding area or the at least one reference area (301b) of the first lithographic element remains substantially uncontaminated. For example, the first lithographic element is a mirror (301) and the second lithographic element is a mask or reticle (303).

  The EUV light source (307) emits EUV light (305) onto the mirror (301). EUV light (305 ') is reflected from this mirror (301) to a mask or reticle (303) by a mirror positioned at an angle α, for example 45 ° ± 6 °. Contaminant (306) present in the vacuum chamber (306) may contaminate at least one test area (301a) of the mirror, but due to a shield positioned on the upper surface of the at least one reference area, At least one reference region (301b) of Also, since the EUV mask includes a mirror, the reticle or mask becomes contaminated by the contaminant (306).

  The second lithographic element, eg mask or reticle, typically becomes scanned during the contamination step. A separate test zone may be defined on the second lithographic element to compare the contamination level between the test areas of the second lithographic element.

  In the next step of the method for measuring contamination of the second lithographic element, the second lithographic element is a reticle or mask and the contaminant is removed from the chamber. If the contamination rate is sufficiently low compared to the contamination measurement time and / or depends on the required measurement accuracy, this step may not be performed. Therefore, these steps are optional. Removing the pollutant means keeping the source away from further contamination. For example, if the contaminant (306) is a gas present in the vacuum chamber, the method may further include removing contaminants present on the system wall, eg, by a vacuum chamber cleaning step, eg, Outbaking can be performed to eliminate these gases. In other words, the method may include an additional step of cleaning the chamber.

  In the next step of the method for measuring contamination of the second lithographic element, the second lithographic element is a reticle or mask and the shielding of at least one reference region of the first lithographic element is removed. Removing the shielding means that what covers at least one reference region is removed (FIG. 3C). This “unshielding” may be performed mechanically, for example, using a shutter that moves away from at least one reference region (301b). After this step, performed after exposure, the first lithographic element includes at least one reference area (301b) that has not changed and at least one test area (301a ') that is contaminated.

  In the next step of the method of measuring contamination of the second lithographic element, the second lithographic element is a reticle or mask, and the contamination level of the second lithographic element is adjusted in-situ, i.e. in the processing chamber. Measured in This measurement is made by redirecting the exposure beam (305) through the reference area of the first lithographic element to the second lithographic element and to the sensor (308). The reference area is no longer shielded or covered.

  During this step, a test value for the parameter is measured, preferably the reflectivity of the contaminated reticle. At wavelengths using a transmission mask, the transmittance of a contaminated reticle or mask may be measured in a similar manner. In this case, a lens is used instead of a mirror to transmit the electromagnetic radiation from the beam source via the first lithographic element towards the second lithographic element and the sensor.

  In one embodiment, contamination of the second lithographic element is measured by measuring optical parameters, such as transmission or reflectance for a reference zone at the second lithographic element and a test zone at the second lithographic element. Or decided. The reference zone at the second lithographic element may be obtained by shielding the second lithographic element, as described above, or may be obtained from a zone on the second lithographic element that is not exposed by the exposure beam. In the latter case, large contamination only occurs in the exposed area, but a small amount of contamination may be present in the reference zone.

  Alternatively, during the step of directing the exposure beam (305) to the uncovered reference region of the first lithographic element, i.e. the second lithographic element and the sensor (308) via the previously coated part, the first lithographic element. The element may move (309). In addition to the reflectivity or transmissivity of the reticle (mask), the reflectivity or transmissivity of the contaminated portion of the first lithographic element, eg, a mirror, can also be considered. It is known that the reticle cap layer may be different from the mirror cap layer. This means that when exposed to contaminants, the reticle may become contaminated in other ways or in other degrees due to the different material properties of the reticle and mirror. By combining reticle contamination, eg, reticle reflectivity, and mirror contamination, eg, mirror reflectivity, the behavior of reticle and / or mirror contamination can be compared and characterized. It is an advantage of the present invention that such characterization can be performed simultaneously in-situ with a single measurement.

  For example, in EUV lithographic measurement, the reflectance of the mirror is preferably about 70%, for example. Due to intentional contamination, the reflectivity of the mirror may degrade by a few percent, typically 1-2%, or even more. As a result, the lifetime of optical elements (mirrors, masks, etc.) is reduced and this is a major concern in lithographs because these optics are extremely expensive. It is important to keep the reflectance change due to contamination as low as possible. Since multiple mirrors are present in the EUV lithographic system, mirror contamination can be further considered when measuring reticle contamination. If only the reticle is contaminated and the mirror is not contaminated, the impact on throughput will be negligible (about 1-2%). To measure the (relative) change in reflectivity of the first and second lithographic elements due to contamination, the reflectivity from at least one test area of the first lithographic element is reflected from at least one reference area of the lithographic element. Compared with rate.

  Furthermore, these reflectivities are compared with the reflectivity of the second lithographic element, which is a mask or reticle. After removing the obstruction from the at least one reference area (301b) of the first lithographic element, at least one (contaminated) test area (301a ′) of the first lithographic element is again exposed by the exposure beam (305). . The beam is reflected from the first lithographic element so that the reflected radiation beam is incident on the second lithographic element (303 '). The reflected light beam reflects from the second lithographic element and is a combination of the reflectance of at least one test area (301a ′) of the first lithographic element and the reflectance of the second lithographic element (303 ′). It goes to the sensor for measuring the test reflectance (FIG. 3C). Because the contaminant is no longer exposed (contaminant has been removed), the contaminant does not affect the reflectivity of the first or second lithographic element.

  In a subsequent step, the movable first lithographic element is moved (309) so that light from the light source exposes at least one reference region (301b) of the first lithographic element. Again, the light reflects from the at least one reference region and travels toward the second lithographic element and further reflects the light beam to reflect the reflectivity of the at least one reference region of the first lithographic element and the reflection of the second lithographic element. Aimed at a sensor that measures the reference reflectance, which is a combination with the rate.

  The difference Δ is the difference between the test reflectance and the reference reflectance. If at least one test area (301a ') is contaminated, a decrease in reflectivity will be measured. If the second lithograph is contaminated, a decrease in reflectivity will be measured. It should be noted that using this in-situ measurement, only relative values of reflectivity can be obtained.

  To obtain absolute reflectance values for at least one test region and at least one reference region, additional reflectance measurements may be performed ex-situ. Alternatively, if DUV radiation is used (instead of EUV radiation), the transmission difference can be measured between at least one test area and at least one reference area.

  According to a second aspect of the present invention, a system for measuring contamination of a lithographic element is provided. The system comprises a processing chamber (501) (see FIG. 5). It comprises means (502) for introducing a first lithographic element into the processing chamber and means for introducing a second lithographic element (503) into the processing chamber. The system includes an energy source within the processing chamber for irradiating first and second lithographic elements introduced into the system. This may further induce contamination of the at least one lithographic element by exposing the at least one lithographic element directly or indirectly to radiation from the energy source (505). Alternatively, the processing chamber may further comprise an inlet for supplying contamination to the processing chamber.

  The system further comprises means for coating at least a portion of the first lithographic element to prevent contamination of the coated portion of the first lithographic element when exposed to the first energy source (505). Provides a reference area on the first lithographic element. The system further comprises a sensor (506) for measuring contamination and an inlet for introducing contaminant (507).

  In this way, the system is adapted to measure a parameter of at least one lithographic element. For example, when using an EUV energy source (505), preferably the processing chamber is under vacuum.

  Furthermore, the system may comprise a second energy source (505 '). In this case, the first energy source (505), eg, a high power energy source, eg, an EUV source, exposes at least one lithographic element directly or indirectly so that contamination of the at least one lithographic element occurs. May be used to A second energy source (505 '), eg, a low power energy source, may be used to measure a parameter, eg, reflectivity, of at least one lithographic element.

  In a preferred embodiment, the contamination is investigated for the area of the lithographic element that has been exposed. This is because pollution is typically strong in these areas. The sensor may be a reflectance sensor or a transmittance sensor, depending on the energy source used. The sensor may include a diode. A system for measuring contamination of lithographic elements may be integrated into a lithographic processing tool, ie a lithographic exposure tool, if possible.

  While preferred embodiments, specific structures and configurations, and materials have been described herein as devices according to the present invention, various changes and modifications in form and detail are possible without departing from the scope and spirit of the invention. Should be understood. For example, the above scheme is merely an example of a procedure that may be used. Functionality may be added or removed from the block diagram, and operations may be exchanged between functional blocks. Steps may be added or deleted from the methods described within the scope of the present invention.

It is a flowchart of a 1st embodiment of the present invention. 2 (a)-(c) illustrate different steps of an embodiment of the present invention for measuring contamination of a first lithographic element. Fig. 4 shows different steps of an embodiment of the invention for measuring contamination of a first lithographic element. 3 (a)-(c) illustrate different steps of an embodiment of the present invention for measuring contamination of the second lithographic element. 1 shows a first lithographic element of the present invention. 1 illustrates a system for measuring contamination of a lithographic element of an embodiment of the present invention.

Claims (29)

A method (100) for measuring contamination of a lithographic element comprising:
Providing a first lithographic element (201, 301) in a processing chamber (101);
Providing (102) a second lithographic element (203, 303) in the processing chamber;
Providing (104) a contaminant (206, 306) into the processing chamber;
A part of the first lithographic element (201, 301) is covered, and a reference area (201b, 301b) that is a covering portion of the first lithographic element (201, 301) is provided in the first lithographic element (201, 301). Providing a test area (201a, 301a), which is an uncovered portion of the first lithographic element (201, 301), in the first lithographic element (201, 301);
After supplying (104) the contaminant (206, 306), the exposure beam (205, 305) is passed through the test area (201a, 301a) of the first lithographic element (201, 301) to the second lithographic element ( 203, 303) such that at least one lithographic element (201, 301, 203, 303) is contaminated by contaminants (206, 306);
Peeling off the covering portion of the first lithographic element (201, 301) to provide an uncovered reference region;
By directing the exposure beam (205, 305) to the sensor (208, 308) via the uncovered reference region (201b, 301b) of the first lithographic element (201, 301) , the first lithograph in the processing chamber. Optically measuring the contamination level of the elements ( 201, 301 ) (106).   The steps of covering a part of the first lithographic element (201, 301) include the installation of a shield (204, 304) covering a part of the first lithographic element (201, 301), and the shielding (204, 304). The method (100) for measuring contamination of a lithographic element according to claim 1, comprising placing a direct contact between at least a portion of the first lithographic element (201, 301).   The step of covering a portion of the first lithographic element (201, 301) comprises installing a shield (204, 304) for creating a shadow on at least a portion of the first lithographic element (201, 301). A method for measuring contamination of the described lithographic elements.   4. The lithographic element contamination according to claim 1, wherein optically measuring the contamination level comprises measuring optical parameters of the test area (201 a, 301 a) and the reference area (201 b, 301 b). How to measure.   The method for measuring contamination of a lithographic element according to any of claims 1 to 4, wherein the first lithographic element (201, 301) is a lithographic optical element.   The lithograph according to any of claims 1-5, further comprising removing contaminants (206, 306) from the processing chamber prior to measuring the contamination level of at least one contaminated lithographic element in the processing chamber. How to measure element contamination.   A method for measuring contamination of a lithographic element according to any of the preceding claims, wherein the at least one contaminated lithographic element is a first lithographic element (201, 301).   The lithographic element contamination according to any of the preceding claims, wherein measuring the contamination level optically comprises measuring optical parameters of the test area (201a, 301a) and the reference area (201b, 301b). How to measure. Measuring the contamination level of the first lithographic element (201, 301) in the processing chamber comprises:
Measuring a value related to the parameter in the uncovered reference area (201b, 301b) of the first lithographic element (201, 301), which is a reference value of the parameter;
Measuring a parameter value in the test area of the first lithographic element (201, 301), which is a test value of the parameter;
A method for measuring contamination of a lithographic element according to any of claims 1 to 8, comprising the step of determining a difference between a reference value and a test value.   The step of measuring the reference value of the parameter comprises the step of directing the exposure beam towards the sensor (208) via the reference area (201b, 301b) of the first lithographic element (201, 301). A method for measuring contamination of the described lithographic elements.   11. Measuring the parameter test value comprises directing the exposure beam to the sensor (208) via the test area (201a) of the first lithographic element (201). A method for measuring contamination of a lithographic element according to claim 1.   12. A method for measuring contamination of a lithographic element according to any of the preceding claims, wherein the second lithographic element (203, 303) is a mask.   The method of measuring contamination of a lithographic element according to any of claims 1 to 12, wherein the second lithographic element (203, 303) comprises a contaminant (206).   14. A lithographic element according to claim 13, wherein the second lithographic element (203, 303) comprises a resist containing a contaminant (206), the contaminant being supplied into the processing chamber by degassing the resist. To measure the pollution of the water.   The second lithographic element (203, 303) directs the exposure beam to the second lithographic element (203, 303) via the test area (201a, 301a) of the first lithographic element (201, 301). A method for measuring contamination of a lithographic element according to any of the preceding claims, wherein in the step, the contamination (206, 306) is contaminated. Method for measuring contamination of a lithographical element according to any one of claims 1 to 15, further comprising the step of measuring the level of contamination of the second lithographical element (203, 303) within the processing chamber. Step to measure the contamination level of the second lithographical element (203, 303) is
By directing the exposure beam towards the second lithographic element (203, 303) via the reference area (201b, 301b) of the first lithographic element and further towards the sensor (208, 308), the second 17. A method for measuring contamination of a lithographic element according to claim 16, comprising the step of measuring a second element test value for a parameter in a test area of the lithographic element (203, 303).   The step of measuring the second element test value is to direct the exposure beam toward the second lithographic element via the test area (201a, 301a) of the first lithographic element and further toward the sensor (208). The method of measuring contamination of a lithographic element according to claim 17 further comprising:   A method for measuring contamination of a lithographic element according to any of the preceding claims, wherein the first lithographic element (201, 301) is a mirror.   20. A method for measuring contamination of a lithographic element according to claim 19, wherein the parameter is the reflectivity of the first lithographic element (201, 301).   21. A method for measuring contamination of a lithographic element according to any of claims 19-20, wherein the sensor (208) is a reflectance sensor.   A method for measuring contamination of a lithographic element according to any of the preceding claims, wherein the first lithographic element (201, 301) is a lens.   The method of measuring contamination of a lithographic element according to claim 22, wherein the parameter is the transmittance of the first lithographic element.   24. A method for measuring contamination of a lithographic element according to any of claims 22 to 23, wherein the sensor (208) is a transmission sensor.   25. A method for measuring contamination of a lithographic element according to any of claims 1 to 24, wherein the test area (201a, 301a) comprises a plurality of test zones.   26. A method for measuring contamination of a lithographic element according to any of the preceding claims, wherein the reference region (201b, 301b) comprises a plurality of reference zones. A system for measuring contamination of lithographic elements,
A processing chamber;
A first lithographic element (201, 301) and a second lithographic element (203, 303);
A contamination source for supplying the contaminants (206, 306);
At least one first and second lithographic elements by directly or indirectly exposing at least one first and second lithographic elements (201, 301, 203, 303) in the presence of contaminants (206, 306). elements (201,301,203,303) energy source for supplying the error Nerugi over beam into the process chamber so as to cause contamination of the (207, 307),
Means (204, 304) for covering at least a part of the first lithographic element (201, 301) to provide a reference area (201b, 301b) in the first lithographic element (201, 301), when the first lithographical element (201, 301) is exposed to error Nerugi over beam, the reference region (201b, 301b) and the covering means to prevent contaminated,
A sensor (208) for receiving an energy beam from the energy source (207, 307) via the reference region (201b, 301b) of the first lithographic element (201, 301) . Energy sources (207, 307), the system for measuring contamination of a lithographical element according to claim 27 which is adapted to emit electromagnetic radiation of extreme ultraviolet range.   29. System for measuring contamination of lithographic elements according to claim 27 or 28, wherein the sensor (208) is an optical sensor.