DE60117107T2 - Lithographic projection apparatus, method of making an article, article and gas composition produced thereby - Google Patents

Description

The present invention relates to a lithographic projection apparatus comprising:
a radiation system for providing a projection beam of radiation;
patterning means for applying a pattern to the projection beam according to a desired pattern;
a substrate table for holding a substrate; and
a projection system for imaging the patterned beam onto a target portion of the substrate.

• – Einen Maskentisch zum Halten einer Maske. Das Konzept einer Maske ist in der Lithographie gut bekannt und umfasst binäre, wechselnde Phasenverschiebungs- und reduzierte Phasenverschiebungsmaskenarten sowie verschiedene Arten von Hybridmasken. Die Anordnung einer derartigen Maske im Strahlungsstrahl bewirkt selektive Lichtdurchlässigkeit (im Falle einer lichtdurchlässigen Maske) bzw. Reflexion (im Falle einer reflektierenden Maske) der auf die Maske auftreffenden Strahlung gemäß dem Muster auf der Maske. Der Maskentisch stellt sicher, dass die Maske in einer gewünschten Position im eingehenden Strahl aus Strahlung gehalten werden kann und dass sie, sofern erwünscht, bezogen auf den Strahl bewegt werden kann.
• – Ein programmierbares Spiegelfeld. Ein Beispiel für ein derartiges Element ist eine matrixadressierbare Oberfläche, die eine viskoelastische Steuerschicht und eine reflektierende Oberfläche aufweist. Das Grundprinzip hinter einer derarti gen Vorrichtung ist, dass (zum Beispiel) adressierte Bereiche der reflektierenden Oberfläche auftreffendes Licht als gebrochenes Licht reflektieren, wohingegen unadressierte Bereiche auftreffendes Licht als ungebrochenes Licht reflektieren. Wird ein geeigneter Filter verwendet, kann das besagte ungebrochene Licht aus dem reflektierten Strahl herausgefiltert werden, wobei nur das gebrochene Licht zurückgelassen wird; auf diese Weise wird der Strahl gemäß dem Adressierungsmuster der matrixadressierbaren Oberfläche gemustert. Die erforderliche Matrixadressierung kann unter Verwendung geeigneter elektronischer Einrichtungen durchgeführt werden. Weitere Informationen über derartige Spiegelfelder können beispielsweise den US-Patenten 5,296,891 und US 5,523,193 entnommen werden, die hierdurch durch Literaturhinweis eingefügt werden.
• – Ein programmierbares LCD-Feld. Ein Beispiel für eine derartige Konstruktion ist im US-Patent 5,229,872 gegeben, das hierdurch durch Literaturhinweis eingefügt wird.

The term "patterning means" should be interpreted to refer to means that can be used to impart a patterned transverse cut to an incoming beam of radiation according to a pattern to be created in a target portion of the substrate; "Light valve" has also been used in this context. In general, said pattern corresponds to a particular functional layer in a device produced in the target section, such as an integrated circuit or other device (see below). Examples of such pattern applying means include:

• - A mask table for holding a mask. The concept of a mask is well known in lithography and includes binary, alternating phase shift and reduced phase shift mask types, as well as various types of hybrid masks. The arrangement of such a mask in the radiation beam causes selective transmission of light (in the case of a translucent mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask according to the pattern on the mask. The mask table ensures that the mask can be held in a desired position in the incoming beam of radiation and, if desired, can be moved relative to the beam.
• - A programmable mirror field. An example of such an element is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such a device is that (for example) addressed areas of the reflective surface reflect incident light as refracted light, whereas unaddressed areas reflect incident light as unbroken light. If a suitable filter is used, the said unbroken light can be filtered out of the reflected beam, leaving only the refracted light behind; in this way, the beam is patterned according to the addressing pattern of the matrix-addressable surface. The required matrix addressing can be performed using appropriate electronic equipment. Further information on such mirror fields can be found, for example, in US Pat. Nos. 5,296,891 and 5,523,193, which are hereby incorporated by reference.
• - A programmable LCD panel. An example of such a construction is given in U.S. Patent 5,229,872, which is hereby incorporated by reference.

Out establish In simplification, the rest of this text may be specific Ask specifically to refer to examples that have a mask table and use a mask; the general principles discussed in these cases However, in the broader context, the patterning device should be used be seen as stated above.

Lithographic projection devices can be used, for example, for the manufacture of integrated circuits (ICs). In such a case, the pattern applying means may generate a circuit pattern corresponding to a single layer of the integrated circuit, and this pattern may be on a target portion (eg containing one or more dies) on a substrate (silicon wafer) coated with a layer of radiation-sensitive material (FIG. Protective varnish) has been coated, be imaged. In general, a single wafer will contain a whole network of adjacent target portions, which will be successively irradiated one at a time by the projection system. In the generally conventional ago directions, where the pattern is applied via a mask on a mask table, it can be distinguished between two different types of machines. In one type of lithographic projection apparatus, each target portion is irradiated by applying the entire mask pattern to the target portion in one step; Such a device is generally referred to as a wafer stepper. In another device - commonly referred to as a step-and-scan device - each target section is irradiated by progressively scanning the mask pattern under the projection beam in a predetermined reference direction (the "scanning" direction) while the substrate table is parallel or Since the projection system generally has a magnification factor M (generally <1), the velocity V at which the substrate table is scanned is a factor M times that of which the mask table is scanned is scanned. Further information regarding lithographic devices as described herein can be found in e.g. US 6,046,792 are taken, which is hereby incorporated by reference.

at a manufacturing process in which a lithographic projection apparatus is used, a pattern (e.g., in a mask) is applied to a substrate imaged at least partially by a layer of radiation-sensitive Material (protective layer) is covered. Before this imaging step the substrate can be subjected to several process steps, such as. Priming, protective coating and a softbake. To exposure, the substrate can be subjected to further process steps be such. a post-exposure bake (PEB), development, a Hardbake and measuring / inspecting the depicted structures. These Sequence of process steps is used as a basis to create a individual layer of a device, e.g. an integrated Circuit to provide a pattern. Such a patterned one Layer can then be subjected to several process steps, e.g. Etching, ion implantation (Doping), metallization, oxidation, chemomechanical polishing etc., all of which serve an individual Finish shift. If multiple layers are required, must have the entire procedure, or a variant of it, for each new one Be repeated layer. Finally there is a group of components on the substrate (wafer). These elements will be then by a method such as Split or saw separately, after which the individual elements mounted on a support, connected with pins can be etc. Further information regarding such process steps can for example the book "Microchip Fabrication: A Practical Guide to Semiconductor Processing ", 3rd Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4 which is incorporated herein by reference.

For the sake of simplicity, the projection system may hereinafter be referred to as a "lens", however, this term should be interpreted to include various types of projection systems including, for example, refractive optics, reflective optics, and caradioptric systems which operate in accordance with each of these types of structures for guiding, shaping or controlling the projection beam of radiation, and such components may also be collectively or individually referred to hereinafter as a "lens". Further, the lithographic apparatus may be such that it has two or more substrate tables (and / or two or more mask tables). In such "multi-stage" devices, the additional tables may be used in parallel, or preparatory steps may be performed on one or more tables while one or more other tables are being used for exposures US 5,969,441 and in WO 98/40791, which are hereby incorporated by reference.

In order to reduce the size of the structures that can be imaged, it is desirable to reduce the wavelength of the exposure radiation. Therefore, wavelengths less than 180nm are used, for example 157nm or 126nm. However, such wavelengths are strongly absorbed by the normal ambient air, resulting in unacceptable loss of intensity as the beam passes through the device. To solve this problem, it has hitherto been proposed to flush the device with a gas stream, wherein the gas, eg nitrogen (N ₂ ), is substantially transparent to the illumination wavelength.

Lithographic projection devices may include interferometric displacement measuring means used to accurately determine the position of slidable tables, such as mask or substrate tables. These means measure the path length (geometric distance x refractive index) to the movable tables using measuring beams of coherent monochromatic radiation. The measuring devices are very sensitive to pressure and temperature fluctuations and changes in the composition of the medium, which pass through the measuring beams. All of these three variables affect the refractive index of the medium. Usually a second harmonic interferometer is used to account for the refractive index changes caused by temperature and pressure variations. Further information regarding such harmonic interferometers, which are able to compensate for temperature and pressure fluctuations, for example, the US 5,404,222 are taken, which is hereby incorporated by reference.

alternative the second harmonic interferometer can change the composition of the medium. However, this second interferometer can the pressure and temperature fluctuations and the changes in the composition of the medium does not take into account simultaneously.

Some rooms of the projection apparatus may be flushed with a cleaning gas to remove any gas, such as oxygen or water, causing radiation at the wavelength of the pro Jektionsstrahls is absorbed from radiation. The inventors have found that when the gas used to rinse the system enters the area in which the interferometric displacement measuring means operate, the refractive index changes in those areas and the position measurements are affected. In order for the measuring means to continue to operate at the high degree of accuracy required, any deviation from the refractive index of the medium must be avoided.

It It is an object of the invention to provide a lithographic projection apparatus to create, in which the escape of cleaning gas interferometric the Displacement measuring means not affected.

• – ein interferometrisches Verschiebungsmessmittel, das bei einer Wellenlänge λ₁ zur Messung der Position des Substrattisches oder der Position eines Tisches, der Teil der Musteraufbringungseinrichtung ist, arbeitet;
• – Spülgasmittel zur Zufuhr von Reinigungsgas in einen Raum, um Umgebungsluft hieraus zu verdrängen, wobei der Raum wenigstens einen Teil des Substrattisches und/oder wenigstens einen Teil des Tisches, der Teil der Musteraufbringungseinrichtung ist, aufnimmt, wobei das Reinigungsgas für den Projektionsstrahl aus Strahlung im Wesentlichen nicht-absorbierend ist und einen Brechungsindex bei einer Wellenlänge λ₁ hat, der im Wesentlichen dem von Luft gleich ist, wenn mit der gleichen Wellenlänge, Temperatur und Druck gemessen wird; und
• – Gaszufuhreinrichtungen, die das Reinigungsgas enthalten.

These and other objects are achieved according to the invention in a lithographic apparatus as specified in the introduction, characterized by:

• An interferometric displacement measuring means operating at a wavelength λ ₁ for measuring the position of the substrate table or the position of a table forming part of the patterning means;
• Purge gas means for supplying purge gas into a space to displace ambient air therefrom, the space receiving at least a portion of the substrate table and / or at least a portion of the table forming part of the patterning means, the purge gas for the projection beam being radiation in the Is substantially non-absorbent and has a refractive index at a wavelength λ ₁ substantially equal to that of air when measured at the same wavelength, temperature and pressure; and
• - Gas supply means containing the cleaning gas.

The Inventors have found that by rinsing, for example, the mask and the substrate carrier, the usually each having movable mask and substrate tables, by means a special gaseous Composition whose refractive index under the same measurement conditions identical to that of air, the interferometric displacement measuring means as required Accuracy level can work, while the application of radiation with a wavelength of 180nm or less allowed is.

wobei F_j der Volumenbruchteil des Bestandteils j im Reinigungsgas ist, wobei das Reinigungsgas insgesamt k Bestandteile enthält; α_j1 das Brechungsvermögen des Bestandteils j bei einer Wellenlänge λ₁ ist, α_j2 das Brechungsvermögen des Bestandteils j bei einer Wellenlänge λ₂ ist, α_j3 das Brechungsvermögen des Bestandteils j bei einer Wellenlänge λ₃ ist, α_a1 das Brechungsvermögen von Luft bei einer Wellenlänge λ₁ ist, α_a2 das Brechungsvermögen von Luft bei einer Wellenlänge λ₂ ist und α_a3 das Brechungsvermögen von Luft bei einer Wellenlänge λ₃ ist; und wobei: According to another embodiment of the invention, there is provided a device as described above comprising a second harmonic interferometric measuring means operating at wavelengths λ ₂ and λ ₃ for adjusting the measurements of the interferometric displacement measuring means to substantially accommodate effects of pressure and temperature variations and wherein the cleaning gas has three or more different components, each component having a refractive power at the wavelengths λ ₂ and λ ₃ such that the following equations are substantially satisfied:

where F _{j is} the volume fraction of component j in the purge gas, the purge gas containing a total of k components; α _{j1 is} the refractive power of the component j at a wavelength λ ₁ , α _{j2 is} the refractive power of the component j at a wavelength λ ₂ , α _{j3 is} the refractive power of the component j at a wavelength λ ₃ , α _{a1 is} the refractive power of air at a Wavelength λ ₁ , α _{a2 is} the refractive power of air at a wavelength λ ₂ , and α _{a3 is} the refractive power of air at a wavelength λ ₃ ; and wherein:

Where a second harmonic interferometer is present in the device, simply adjusting the refractive index of the cleaning gas to that of air at the operating wavelength of the interferometric displacement meter is insufficient to eliminate the errors in displacement measurement caused by leakage of cleaning gas , The inventors of the present invention have therefore created a cleaning gas composition which discriminates at least three Each constituent usually has a significantly different refractive power (the refractive power being defined as the refractive index-1). If the gases are properly selected so that the gases meet or substantially meet the equations above, the change in cleaning gas will have no or substantially no effect on the measurements of each of the interferometers in terms of their composition. Thus, accurate position measurements can be achieved, which take into account the changes in temperature, pressure and leakage of cleaning gas.

• – ein interferometrisches Verschiebungsmessmittel, das bei einer Wellenlänge λ₁ zur Messung der Position des Substrattisches oder der Position eines Tisches, der Teil der Musteraufbringungseinrichtung ist, arbeitet;
• – ein zweites harmonisches interferometrisches Messmittel, welches bei Wellenlängen λ₂ und λ₃ zur Einstellung der Messungen des interferometrischen Verschiebungsmessmittels arbeitet, um im Wesentlichen Auswirkungen von Druck- und Temperaturschwankungen zu eliminieren;
• – Spülgasmittel zur Zufuhr von Reinigungsgas in einen Raum, um Umgebungsluft hieraus zu verdrängen, wobei der Raum zumindest einen Teil des Substrattisches und/oder zumindest einen Teil des Tisches aufnimmt, der Teil der Musteraufbringungseinrichtung ist, wobei das Reinigungsgas für den Projektionsstrahl aus Strahlung im Wesentlichen nicht-absorbierend ist und zwei oder mehr Bestandteile aufweist, wobei jeder Bestandteil ein Brechungsvermögen bei Wellenlängen λ₁, λ₂ und λ₃ aufweist, die so sind, dass die folgende Gleichung im Wesentlichen erfüllt ist:
  
  wobei α_m1 das Brechungsvermögen des Reinigungsgases bei einer Wellenlänge λ₁ ist, α_m2 das Brechungsvermögen des Reinigungsgases bei einer Wellenlänge λ₂ ist, α_m3 das Brechungsvermögen des Reinigungsgases bei einer Wellenlänge λ₃ ist und
  
  wobei α_a1 das Brechungsvermögen von Luft bei einer Wellenlänge λ₁ ist, α_a2 das Brechungsvermögen von Luft bei einer Wellenlänge λ₂ und α_a3 das Brechungsvermögen von Luft bei einer Wellenlänge λ₃ ist; und
• – Gaszufuhrmittel, welche das Reinigungsgas aufweisen.

According to another aspect of the invention, there is provided a lithographic apparatus as described in the introduction, characterized by:

• An interferometric displacement measuring means operating at a wavelength λ ₁ for measuring the position of the substrate table or the position of a table forming part of the patterning means;
• A second harmonic interferometric measuring means operating at wavelengths λ ₂ and λ ₃ for adjusting measurements of the interferometric displacement measuring means to substantially eliminate effects of pressure and temperature variations;
• Purge gas means for supplying purge gas into a space to displace ambient air therefrom, the space receiving at least a portion of the substrate table and / or at least a portion of the table forming part of the patterning means, the purge gas for the projection beam being substantially radiation non-absorbent and having two or more constituents, each constituent having a refractive power at wavelengths λ ₁ , λ ₂ and λ ₃ such that the following equation is substantially satisfied:
  
  where α _{m1 is} the refracting power of the purifying gas at a wavelength λ ₁ , α _{m 2} is the refracting power of the purifying gas at a wavelength λ ₂ , α _{m3 is} the refractive power of the purifying gas at a wavelength λ ₃ , and
  
  where α _{a1 is} the refractive power of air at a wavelength λ ₁ , α _{a2 is} the refractive power of air at a wavelength λ _2, and α _{a3 is} the refractive power of air at a wavelength λ ₃ ; and
• - Gas supply means having the cleaning gas.

at This aspect is neither the interferometric displacement measuring means nor the second harmonic interferometer required to one to provide accurate measurement of cleaning gas contamination considered. Rather, this aspect ensures that the entire interferometric System is set to allow for the impact of cleaning gas impurities Takes into account. This is achieved by the errors in the interferometric displacement measuring means be added to those of the second harmonic interferometer. This aspect of the invention provides an alternative way in which the effects of temperature, pressure and exit of cleaning gas accurately take into account the interferometer measurements and it allows a simpler mixture of gases, e.g. just two different gases, to use.

• – Spülgasmittel zur Zufuhr von Reinigungsgas in einen Raum, um Umgebungsluft hieraus zu verdrängen, wobei der Raum wenigstens einen Teil des Substrattisches und/oder wenigstens einen Teil des Tisches aufnimmt, der Teil der Musteraufbringseinrichtung ist, wobei das Reinigungsgas für den Projektionsstrahl aus Strahlung im Wesentlichen nicht-absorbierend ist;
• – ein interferometrisches Verschiebungsmessmittel, das bei einer Wellenlänge λ₁ zur Messung der Position des Substrattisches oder der Position eines Tisches, der Teil der Musteraufbringungseinrichtung ist, arbeitet; und
• – ein zweites harmonisches interferometrisches Messmittel, welches bei Wellenlängen λ₂ und λ₃ arbeitet, um die Messungen des interferometrischen Verschiebungsmessmittels (DI) gemäß der folgenden Gleichung einzustellen: L = (DI) – K(SHI) (9)wobei L die eingestellte Messung des interferometrischen Verschiebungsmessmittels ist, SHI die Messung des zweiten harmonischen interferometrischen Verschiebungsmessmittels ist und K ein Koeffizient ist, dessen Wert so optimiert ist, dass Auswirkungen von Änderungen in Druck, Temperatur und Reinigungsgaszusammensetzung teilweise von der eingestellten Messung L eliminiert sind.

According to a further aspect of the invention, there has been provided a lithographic apparatus as described in the introduction, characterized by

• Purge gas means for supplying purge gas into a space to displace ambient air therefrom, the space receiving at least a portion of the substrate table and / or at least a portion of the table being part of the pattern applicator, the cleaning gas for the projection beam being substantially radiation non-absorbent;
• An interferometric displacement measuring means operating at a wavelength λ ₁ for measuring the position of the substrate table or the position of a table forming part of the patterning means; and
• A second harmonic interferometric measuring means operating at wavelengths λ ₂ and λ ₃ for adjusting the measurements of the interferometric displacement measuring means (DI) according to the following equation: L = (DI) - K (SHI) (9) where L is the set measurement of the interferometric displacement measuring means, SHI is the measurement of the second harmonic interferometric displacement measuring means and K is a coefficient whose value is optimized so that effects of changes in pressure, temperature and purge gas composition are partially eliminated from the set measurement L.

at In this aspect of the invention, the coefficient K is optimized to the least possible mistake in the length measurement L to surrender This embodiment is regarding the specific combinations of gases used can be less demanding than the first three embodiments of the invention and therefore provides a more cost effective way by which the errors due to the change of Composition of the cleaning gas can be reduced.

• – Bereitstellen eines Substrats, das wenigstens teilweise mit einer Schicht aus strahlungsempfindlichem Material bedeckt ist;
• – Bereitstellen eines Projektionsstrahls aus Strahlung unter Verwendung eines Strahlungssystems;
• – Verwendung von Musteraufbringungseinrichtungen, um dem Projektionsstrahl in seinem Querschnitt ein Muster aufzuprägen;
• – Projizieren des gemusterten Strahls aus Strahlung auf einen Zielbereich der Schicht aus strahlungsempfindlichem Material, gekennzeichnet durch folgende Schritte
• – Bestimmen der Position eines Tisches unter Verwendung interferometrischer Verschiebungsmessmittel, die bei einer Wellenlänge λ₁ arbeiten, wobei der Tisch entweder zum Halten des Substrats geeignet ist oder Teil der Musteraufbringungseinrichtung bildet;
• – Liefern von Reinigungsgas in einen Raum, der wenigstens einen Teil des Tisches aufnimmt, um Umgebungsluft hieraus zu verdrängen, wobei das Reinigungsgas für den Projektionsstrahl aus Strahlung im Wesentlichen nicht-absorbierend ist und bei einer Wellenlänge λ₁ einen Brechungsindex hat, der im Wesentlichen dem von Luft, gemessen bei der gleichen Wellenlänge, Temperatur und Druck gleich ist.

According to a further aspect of the invention, there has been provided a method of manufacturing a device, comprising the steps of:

• Providing a substrate that is at least partially covered by a layer of radiation-sensitive material;
• Providing a projection beam of radiation using a radiation system;
• Using patterning means to impart a pattern to the projection beam in its cross section;
• Projecting the patterned beam of radiation onto a target area of the layer of radiation-sensitive material, characterized by the following steps
• Determining the position of a table using interferometric displacement measuring means operating at a wavelength λ ₁ , the table being either suitable for holding the substrate or forming part of the patterning means;
• Supplying cleaning gas into a space receiving at least a portion of the table to displace ambient air therefrom, the cleaning gas for the projection beam of radiation being substantially non-absorbent and having a refractive index at a wavelength λ ₁ substantially equal to that of of air, measured at the same wavelength, temperature and pressure is the same.

wobei F_j ein Volumenbruchteil des Bestandteils j in dem Reinigungsgas ist, wobei das Reinigungsgas eine Gesamtrahl von k Bestandteilen enthält, α_j1 das Brechungsvermögen des Bestandteils j bei einer Wellenlänge λ₁ ist, α_j2 das Brechungsvermögen des Bestandteils j bei einer Wellenlänge λ₂ ist, α_j3 das Brechungsvermögen des Bestandteils j bei einer Wellenlänge λ₃ ist, α_a1 das Brechungsvermögen von Luft bei einer Wellenlänge λ₁ ist, α_a2 das Brechungsvermögen von Luft bei einer Wellenlänge λ₂ und α_a3 das Brechungsvermögen von Luft bei einer Wellenlänge λ₃ ist, und wobei: In a preferred embodiment, the method further comprises the step of adjusting the measurement of the interferometric displacement measuring means to substantially eliminate effects of pressure and temperature variations using a second harmonic interferometric measuring means operating at wavelengths λ ₂ and λ ₃ . In this embodiment, the cleaning gas has three or more different constituents, each constituent having such a refractive power at the wavelengths λ ₂ and λ ₃ that the following equations are substantially satisfied:

where F _{j is} a volume fraction of the component j in the cleaning _gas , the cleaning _gas containing a total _beam of k components, α _{j1 is} the refractive power of the component j at a wavelength λ ₁ , α _{j2 is} the refractive power of the component j at a wavelength λ ₂ , α _{j3 is} the refractive power of the component j at a wavelength λ ₃ , α _{a1 is} the refractive power of air at a wavelength λ ₁ , α _{a2 is} the refractive power of air at a wavelength λ ₂ and α _{a3 is} the refractive power of air at a wavelength λ ₃ , and wherein:

• – Bereitstellen eines Substrats, das wenigstens teilweise mit einer Schicht aus strahlungsempfindlichem Material bedeckt ist;
• – Bereitstellen eines Projektionsstrahls aus Strahlung unter Verwendung eines Strahlungssystems;
• – Verwendung von Musteraufbringungseinrichtungen, um dem Projektionsstrahl in seinem Querschnitt ein Muster aufzuprägen;
• – Projizieren des gemusterten Strahls aus Strahlung auf einen Zielbereich der Schicht aus strahlungsempfindlichem Material, gekennzeichnet durch folgende Schritte
• – Bestimmen der Position eines Tisches unter Verwendung einer interferometrischen Verschiebungsmesseinrichtung, die bei einer Wellenlänge λ₁ arbeitet, wobei der Tisch entweder zum Halten des Substrats geeignet ist oder Teil der Musteraufbringungseinrichtung bildet;
• – Einstellen der Messung der interferometrischen Verschiebungsmesseinrichtung, um die Auswirkungen von Änderungen in Druck und Temperatur im Wesentlichen zu eliminieren, indem ein zweites harmonisches interferometrisches Messmittel verwendet wird, welches bei Wellenlängen λ₂ und λ₃ arbeitet;
• – Liefern von Reinigungsgas in einen Raum, der wenigstens einen Teil des Tisches aufnimmt, um Umgebungsluft hieraus zu verdrängen, wobei das Reinigungsgas für den Projektionsstrahl aus Strahlung im Wesentlichen nicht-absorbierend ist und zwei oder mehr Bestandteile aufweist, wobei jeder Bestandteil ein Brechungsvermögen bei den Wellenlängen λ₁, λ₂ und λ3 aufweist, die so sind, dass die folgende Gleichung im Wesentlichen erfüllt ist:
  
  wobei α_m1 das Brechungsvermögen des Reinigungsgases bei einer Wellenlänge λ₁ ist, α_m2 das Brechungsvermögen des Reinigungsgases bei einer Wellenlänge λ₂ ist, α_m3 das Brechungsvermögen des Reinigungsgases bei einer Wellenlänge λ₃ ist und
  
  wobei α_a1 das Brechungsvermögen von Luft bei einer Wellenlänge λ₁ ist, α_a2 das Brechungsvermögen von Luft bei einer Wellenlänge λ₂ und α_a3 das Brechungsvermögen von Luft bei einer Wellenlänge λ₃ ist.

Another aspect of the invention provides a method of making a device comprising the steps of:

• Providing a substrate that is at least partially covered by a layer of radiation-sensitive material;
• Providing a projection beam of radiation using a radiation system;
• Using patterning means to impart a pattern to the projection beam in its cross section;
• Projecting the patterned beam of radiation onto a target area of the layer of radiation-sensitive material, characterized by the following steps
• Determining the position of a table using an interferometric displacement measuring device operating at a wavelength λ ₁ , the table being either suitable for holding the substrate or forming part of the patterning device;
• - adjusting the measurement of the interferometric displacement measuring device to substantially eliminate the effects of changes in pressure and temperature by using a second harmonic interferometric measuring means operating at wavelengths λ ₂ and λ ₃ ;
• Supplying cleaning gas into a space accommodating at least a portion of the table to displace ambient air therefrom, the projection beam cleaning gas being substantially non-absorbent of radiation and having two or more constituents, each constituent having a refractive power in the Wavelengths λ ₁ , λ ₂ and λ ₃ , which are such that the following equation is substantially satisfied:
  
  where α _{m1 is} the refracting power of the purifying gas at a wavelength λ ₁ , α _{m 2} is the refracting power of the purifying gas at a wavelength λ ₂ , α _{m3 is} the refractive power of the purifying gas at a wavelength λ ₃ , and
  
  where α _{a1 is} the refractive power of air at a wavelength λ ₁ , α _{a2 is} the refractive power of air at a wavelength λ _2, and α _{a3 is} the refractive power of air at a wavelength λ ₃ .

• – Bereitstellen eines Substrats, das wenigstens teilweise mit einer Schicht aus strahlungsempfindlichem Material bedeckt ist;
• – Bereitstellen eines Projektionsstrahls aus Strahlung unter Verwendung eines Strahlungssystems;
• – Verwendung von Musteraufbringungseinrichtungen, um dem Projektionsstrahl in seinem Querschnitt ein Muster aufzuprägen;
• – Projizieren des gemusterten Strahls aus Strahlung auf einen Zielbereich der Schicht aus strahlungsempfindlichem Material, gekennzeichnet durch folgende Schritte
• – Liefern von Reinigungsgas in einen Raum, der wenigstens einen Teil eines Tisches aufnimmt, um Umgebungsluft hieraus zu verdrängen, wobei der Tisch entweder geeignet ist zum Halten des Substrats oder einen Teil der Musteraufbringungseinrichtung bildet, wobei das Reinigungsgas für den Projektionsstrahl aus Strahlung im Wesentlichen nicht-absorbierend ist;
• – Bestimmen der Position des Tisches unter Verwendung eines interferometrischen Verschiebungsmessmittels, das bei einer Wellenlänge λ₁ arbeitet; und
• – Einstellen der Messung des interferometrischen Verschiebungsmessmittels (DI) unter Verwendung eines zweiten harmonischen interferometrischen Messmittels, das bei Wellenlängen λ₂ und λ₃ arbeitet, gemäß der folgenden Gleichung: L = (DI) – K(SHI), (9) wobei L die eingestellte Messung dersinterferometrischen Verschiebungsmessmittels ist, SHI die Messung des zweiten interferometrischen Messmittels ist und K ein Koeffizient ist, dessen Wert so optimiert ist, dass die Auswirkungen von Änderungen in Druck, Temperatur und Zusammensetzung des Reinigungsgases aus dem eingestellten Wert L teilweise eliminiert sind.

Another aspect of the invention provides a method of making a device comprising the steps of:

• Providing a substrate that is at least partially covered by a layer of radiation-sensitive material;
• Providing a projection beam of radiation using a radiation system;
• Using patterning means to impart a pattern to the projection beam in its cross section;
• Projecting the patterned beam of radiation onto a target area of the layer of radiation-sensitive material, characterized by the following steps
• Supplying cleaning gas into a space accommodating at least part of a table to displace ambient air therefrom, the table being either suitable for holding the substrate or forming part of the patterning means, the cleaning gas for the projection beam being substantially non-radiation -absorbing;
• Determining the position of the table using an interferometric displacement measuring means operating at a wavelength λ ₁ ; and
• - Setting the measurement of the interferometric displacement measuring means (DI) using a second harmonic interferometric measuring means which operates at wavelengths λ ₂ and λ ₃ , according to the following equation: L = (DI) - K (SHI), (9) where L is the set measurement of the interferometric displacement measuring means, SHI is the measurement of the second interferometric measuring means and K is a coefficient whose value is optimized so that the effects of changes in pressure, temperature and composition of the cleaning gas are partially eliminated from the set value L. ,

While reference may be made in this text to the application of the inventive device in the manufacture of integrated circuits, it should be understood that such device may have other uses, such as for the manufacture of integrated optical devices Systems for storing and detecting magnetic bubble memories, liquid crystal displays (LCDs), thin film magnetic heads, and the like. Those skilled in the art will recognize that in the context of such alternative applications, any use of the terms "reticle", "wafer" or "die" in this text has been replaced by the more general terms "mask", "substrate", and "target portion".

in the This document deals with the terms illuminating radiation and lighting beam used to electromagnetic all kinds Radiation, including ultraviolet radiation (e.g., having a wavelength of 365, 248, 193, 157 and 126nm) and EUV as well as particle beams such as e.g. ion beams or electron beams.

in the Following are embodiments the invention only by way of example with reference to the accompanying drawings described, wherein:

1 shows a lithographic projection apparatus according to an embodiment of the invention;

2 the mask support of the lithographic projection apparatus of 1 in detail represents; and

3 the substrate carrier of the lithographic projection apparatus of 1 in detail represents.

In The figures show corresponding reference numerals corresponding parts at.

Embodiment 1

• – ein Strahlungssystem LA, Ex, IL zum Bereitstellen eines Projektionsstrahls PB aus Strahlung (z.B. UV- oder EUV-Strahlung, beispielsweise Strahlung mit einer Wellenlänge von weniger als 180nm, z.B. ca. 157nm oder 126nm);
• – einen ersten Objekttisch (Maskentisch) MT, der einen Maskenhalter zum Halten einer Maske MA (z.B. ein Retikel) aufweist und mit einer ersten Positioniereinrichtung zur genauen Positionierung der Maske bezogen auf den Gegenstand PL verbunden ist;
• – einen zweiten Objekttisch (Substrattisch) WT, der einen Substrathalter zum Halten eines Substrats W (z.B. einen mit einer Schutzschicht bedeckten Wafer) W aufweist und der mit einer zweiten Positioniereinrichtung zur genauen Positionierung des Substrats bezogen auf den Gegenstand PL verbunden ist;
• – ein Projektionssystem („Linse") PL (z.B. einebrechendes oder katadioptrisches System eines Spiegelfeldes) zum Abbilden eines bestrahlten Bereichs der Maske MA auf einen Zielabschnitt C (der ein oder mehrere Dies umfasst) des Substrats W.

1 is a schematic representation of a lithographic projection apparatus according to a particular embodiment of the invention. The apparatus includes:

• A radiation system LA, Ex, IL for providing a projection beam PB of radiation (eg UV or EUV radiation, for example radiation having a wavelength of less than 180 nm, for example approximately 157 nm or 126 nm);
• A first stage (mask table) MT having a mask holder for holding a mask MA (eg, a reticle) and connected to a first positioning means for accurately positioning the mask with respect to the object PL;
• A second stage (substrate table) WT having a substrate holder for holding a substrate W (eg, a wafer covered with a protective layer) W and connected to a second positioning means for accurately positioning the substrate with respect to the object PL;
• A projection system ("lens") PL (eg, a burglar or catadioptric system of a mirror array) for imaging an irradiated area of the mask MA onto a target portion C (comprising one or more dies) of the substrate W.

Of the Apparatus shown here is a light transmitting device (i.e. he has a translucent mask on). However, it may also be reflective in general, for example (with a reflective mask). Alternatively, the apparatus have other patterning means, such as e.g. a programmable Mirror field of a kind as mentioned above).

The Radiation system includes a source LA (e.g., a halogen lamp or an excimer laser) that produces a beam of radiation. This beam is input to an illumination system (Illuminator) IL, either directly or after having conditioning means such as e.g. has passed through a beam expander Ex. The Illuminator IL points Adjustment means AM for adjusting the outer and / or inner radial Expansion (generally referred to as σ-outside and σ-inside) of the intensity distribution in the beam. additionally it comprises various other components, e.g. an integrator IN and a condenser CO. This way it points to the mask MA impinging beam PB in its cross-section a desired uniformity and intensity distribution on.

Regarding 1 It should be noted that the source LA may be located in the housing of the lithographic projection apparatus (as is often the case when the source LA is a mercury lamp, for example), but it may also be remote from the lithographic projection apparatus with the radiation beam, the it is generated, guided into the apparatus (eg with the help of suitable straightening mirrors); the latter scenario is often the case when the source LA is an excimer laser. The present invention and claims include both of these scenarios.

Thereafter, the beam PB impinges on the mask MA, which is held in a mask holder on a mask table MT. After passing through the mask MA, the beam PB passes through the lens PL, which focuses the beam PB on a target portion C of the substrate W. With the help of the second positioning device (and the interferometric measuring device IF, which includes an interferometric displacement measuring means operating at a wavelength λ ₁ , eg at about 633 nm), the substrate table WT can be accurately shifted, eg around different target sections C in the path of the beam PB to position. Similarly, the first positioning means may be used to accurately position the mask MA with respect to the path of the beam PB, eg, after the mask MA has been mechanically fetched from a mask library or during a scan operation. In general, the movement of the object tables MT, WT is realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which in 1 have not been explicitly shown. However, in the case of a wafer stepper (as opposed to a step-and-scan device), the mask table MT may only be connected to a short-stroke trigger or may be fixed.

• 1. Im Step-Modus wird der Maskentisch MA im wesentlichen stationär gehalten, und es wird ein ganzes Maskenbild in einem Schritt (d.h. mit einem einzigen „Flash") auf einen Zielabschnitt C projiziert. Dann wird der Substrattisch WT in X- und/oder Y-Richtung verschoben, so dass ein anderer Zielabschnitt C vom Strahl PB bestrahlt wird.
• 2. Im Scan-Modus geschieht im wesentlichen das gleiche, mit der Ausnahme, dass ein bestimmter Zielabschnitt C nicht durch einen einzigen „Flash" belichtet wird. Stattdessen ist der Maskentisch MT in einer bestimmten Richtung (der sogenannten „Scan-Richtung", z.B. der X-Richtung) mit einer Geschwindigkeit ν verschiebbar, so dass der Projektionsstrahl PB dazu gebracht wird, ein Maskenbild abzutasten; gleichzeitig wird der Substrattisch WT mit einer Geschwindigkeit V = Mν simultan in die gleiche oder die entgegengesetzte Richtung bewegt, wobei M die Vergrößerung der Linse PL ist (gewöhnlich: M = 1/4 oder 1/5). Auf diese Weise kann ein relativ großer Zielabschnitt C belichtet werden, ohne dass Kompromisse hinsichtlich der Auflösung gemacht werden müssen.

The device shown can be used in two different ways:

• 1. In the step mode, the mask table MA is kept substantially stationary, and an entire mask image is projected onto a target portion C in one step (ie, with a single "flash"), then the substrate table WT is X and / or Y direction shifted so that another target portion C is irradiated by the beam PB.
• 2. In scan mode, essentially the same happens, except that a particular target portion C is not exposed by a single "flash." Instead, the mask table MT is in a particular direction (the so-called "scan direction", eg the X direction) at a speed v, so that the projection beam PB is made to scan a mask image; at the same time, the substrate table WT is simultaneously moved in the same or opposite direction at a speed V = Mν, where M is the magnification of the lens PL (usually: M = 1/4 or 1/5). In this way, a relatively large target portion C can be exposed without having to compromise on the resolution.

2 shows the mask carrier with mask table MT of the lithographic apparatus according to the invention in more detail.

As can be seen, the mask M is held in a recess in the mask table MT, which can be made of a ceramic material such as Zerodur (RTM) and positioned by a drive system (not shown) during operation of the lithographic apparatus. The mask table MT is located exactly between the last element of the self-adjusting optics CO, which generates the projection beam PB, and the first element of the projection lens system PL, which projects the projection beam PB onto the wafer W after passing through the mask M (in FIGS 1 and 3 ) Shown.

The mask wearer can enter areas or spaces as follows 2 to 6 be divided: room 2 is located between the final illumination optics CO and the mask table MT; room 3 is located inside the mask table MT above the mask M; room 4 is located within the mask table MT between the mask M and the pellicle 13 ; room 5 is located inside the mask table MT under the pellicle 13 ; and space 6 is located between the mask table MT and the projection lens system PL. Each of the rooms is flushed with a cleaning gas, which is supplied by a gas supply 11 via appropriate flow rate controllers 112 to 116 provided. On the other side of each room, the cleaning gas gets into the container 12 via appropriate vacuum pumps 122 to 126 dissipated. The container 12 may be subdivided to allow controlled reuse of the gas in selected rooms and may be a device 12a for purifying the treated gas.

If desired, the individual spaces of the mask wearer may be separated from each other to ensure laminar flow. For example, a thin film 14 , For example, be provided from CaF or molten SiO ₂ to cover the recess in the mask table MT and space 2 of space 3 to separate. Likewise, films can 15 and 16 used to space 5 and 6 to separate each other and to cover the uneven surface of the first element of the projection lens system PL, respectively.

To the gas flow to the rooms 3 . 4 and 5 be supplied within the mask table MT and remove it again, suitable Lei lines are provided in the body of the mask table. When the mask table has been exposed to air, eg, after a period of inactivity of the device or after replacement of the mask, a purge gas is supplied for a short time before exposure is performed flush any air that might have accumulated in uneven areas of the mask table, for example.

3 shows the wafer carrier of the lithographic apparatus of 1 , To avoid having to provide a path for purge gas that covers the entire range of motion of the wafer carrier, the outputs are 17 for the cleaning gas supply and the inputs 18 attached to the discharge at the lower end of the projection lens system PL on each side of the final element. The exits 17 and the entrances 18 are each with the gas supply 11 and the container 12 via the flow regulator 117 and the vacuum pump 127 each connected. In particular, the outputs 17 , but also the entrances 18 , may be provided with wings for guiding the cleaning gas flow. If not already flat, the final element of the projection lens system PL can be covered with a thin foil as discussed above.

The above flow regulators 112 to 117 may have a static or adjustable pressure or flow restrictor and / or blower as desired to provide the required gas flow rate for the particular embodiment and available gas supply.

According to the invention, the mask carrier and / or the substrate carrier of the device can be flushed with a cleaning gas. The purge gas is usually a mixture of two or more gases selected from N ₂ , He, Ne, Ar, Kr and Xe. The gas composition used is one which is substantially transparent to UV radiation of the wavelength of the projection beam and has a refractive index substantially equal to that of air, provided that it has been measured under the same temperature and pressure conditions (eg cleanroom standard conditions ) and radiation of the same wavelength ver used. The refractive index should be equal to that of air at the wavelength of a radiation beam as used in the interferometric displacement gauge IF. The pressure of the cleaning gas in the mask and / or substrate support may be atmospheric pressure or may be above atmospheric so that any leakage will tend to leak gas rather than contaminating the system with incoming air.

wobei n_j1 der Brechungsindex des Reinigungsgases j bei einer Wellenlänge λ₁ ist.In order to determine which gas mixtures can be used in the present invention, the refractive index of the mixture must be known. The refractive index n _{1 of} a mixture of k gases at a specific partial pressure, temperature and a wavelength λ ₁ can be determined by the following equation:

where n _{j1 is} the refractive index of the cleaning _gas j at a wavelength λ ₁ .

The refractive index α is related to the refractive index n via the equation: α 1 = n 1 - 1 (6a)

wobei F_j die relative Volumenkonzentration des Gases j ist und α_j1 das Brechungsvermögen des unvermischten Gases j bei einer Wellenlänge λ₁ ist. Somit müssen für diese Ausführungsform der vorliegenden Erfindung, wenn das Reinigungsgas aus einem Gasgemisch aus Gasen x und y besteht, die relativen Volumenkonzentrationen der beiden Gase mit folgender Gleichung übereinstimmen: αa1 = Fxαx1 + Fyαy1 (8)wobei α_a1 das Brechungsvermögen von Luft bei einer Wellenlänge λ₁ ist. Oder, um es allgemeiner auszudrücken:

wobei F_j, α_j1 und α_a1 wie vorstehend definiert sind und wobei Consequently, for the mixture of k gases

where F _{j is} the relative volume concentration of the gas j and α _{j1 is} the refractive power of the unmixed gas j at a wavelength λ ₁ . Thus, for this embodiment of the present invention, when the purge gas is a gaseous mixture of gases x and y, the relative volume concentrations of the two gases must conform to the following equation: α a1 = F x α x1 + F y α y1 (8th) where α _{a1 is} the refractive power of air at a wavelength λ ₁ . Or, to put it more generally:

wherein F _j , α _j1 and α _{a1 are} as defined above and wherein

Refractivity and refractive indices depend on pressure, temperature and wavelength, therefore all values of n and α in the above equations as well as in all other equations referred to herein must refer to the same temperature and pressure. Normally, standard conditions are used for clean rooms. The wavelength λ ₁ used for the calculations should be the same as the at least one radiation beam of the interferometric displacement measuring means.

Suitable gas mixtures that conform to this equation include mixtures of N ₂ and either 1 to 5 volume percent He, preferably 2 to 3 volume percent He; 1 to 5% by volume of Ne, preferably 3.5 to 2.5% by volume of Ne; or 35 to 50 volume percent Ar, preferably 40 to 45 volume percent Ar; Mixtures of Ar and 1 to 5 volume percent Xe, preferably 2 to 3 volume percent Xe; Mixtures of Ar and 5 to 10% by volume Kr, preferably 6 to 8% by volume Kr; and mixtures of N ₂ , 0.5 to 3% by volume He and 0.5 to 3% by volume Xe. Preferred gas mixtures for use at a wavelength λ ₁ of 633 nm include those included in the following Table 1. All numbers refer to volume percentages.

Table 1:

Embodiment 2

at this embodiment of the invention, which is the same as the first embodiment except for described below includes the interferometric measuring means IF an interferometric displacement measuring device and a second harmonic interferometric device. The second harmonic interferometric device measures the refractive power of the the atmosphere in the device at two different wavelengths. On this way you can determines the effects of pressure and temperature on the refractive power and therefore the measurement of the displacement interferometer be adjusted accordingly to account for such fluctuations to be able to carry.

This is achieved by multiplying the measurement of the second harmonic interferometer by a coefficient K _a and then subtracting that value from the interferometric displacement measurement. Consequently, the corrected length L is given by L = (DI) -K a (SHI) (9) where DI is the interferometric displacement measurement and SHI is the second harmonic interferometric measurement, where DI and SHI are corrected for operation in average air.

wobei α_ay das Brechungsvermögen von Luft bei einer Wellenlänge λ_y ist und wobei das interferometrische Verschiebungsmessmittel bei einer Wellenlänge λ₁. betätigt wird und das zweite harmonische interferometrische Messmittel bei Wellenlängen λ₂ und λ₃ betätigt wird, wobei die Wellenlänge λ₂ gewöhnlich größer ist als die Wellenlänge λ₃. Beispielsweise kann λ₂ um 532nm und λ₃ um 266nm liegen. Gewöhnlich unterscheidet sich λ₁ von λ₂ und λ₃. λ₁ kann λ₂ oder λ₃ jedoch gleich sein.The coefficient Ka is determined as follows:

wherein α _{ay is} the refractive power of air at a wavelength λ _y and wherein the interferometric displacement measuring means at a wavelength λ ₁ . is actuated and the second harmonic interferometric measuring means at wavelengths λ ₂ and λ _{3 is} actuated, wherein the wavelength λ _{2 is} usually greater than the wavelength λ ₃ . For example, λ ₂ may be around 532nm and λ ₃ around 266nm. Usually, λ ₁ differs from λ ₂ and λ ₃ . However, λ ₁ may be equal to λ ₂ or λ ₃ .

The Setting the interferometric displacement measurement guaranteed in this way, that the position measurement is not affected by temperature and pressure fluctuations inside the lithographic apparatus being affected.

wobei F, α, j und k wie vorstehend definiert sind.The selection of a cleaning gas having a refractive index equal to that of air at a wavelength λ ₁ ensures that the interferometric displacement measuring means is accurate even when cleaning gas enters the measurement area. However, the entry of cleaning gas can cause further significant inaccuracies in the measurements of the refractive power at the wavelengths λ ₂ and λ ₃ with which the second harmonic interferometer operates. This in turn can lead to errors in the final position measurement. The present inventive embodiment addresses this problem by ensuring that the entry of the cleaning gas has no impact on any of the interferometric devices. This can be accomplished by using a purge gas with k gases, where k is three or more, and satisfying or substantially satisfying the following three equations:

wherein F, α, j and k are as defined above.

By simultaneously solving the above three equations, the required fraction of each of the gases j can be determined. The fulfillment of equation (1) ensures that the refractive index (or the refractive index) of the mixture at a wavelength λ ₁ is equal to that of air when measured at the same wavelength, temperature and pressure.

Suitable gas mixtures for use in this embodiment include mixtures of three or more components with different refractive powers. For example, the cleaning gas may comprise one or more components having a refractive power of less than 1 × 10 ^-4 at a wavelength of 200 to 700 nm or two or more components having a refractive power of more than 1 × 10 ^-4 at a wavelength of 200 to 700 nm , Usually, the component having a refractive power of less than 1 × 10 ^-4 at a wavelength of 200 to 700 nm is of the order of 1 to 40, preferably 2 to 20 volume percent, and the two or more components having a refractive power of more than 1 × 10 ^-4 at a wavelength of 200 to 700 nm are present in the range of 60 to 99, preferably 80 to 98 percent by volume.

The purge gas may comprise, for example, three or more gases selected from N ₂ , He, Ne, Ar, Kr and Xe. Usually, the purge gas consists of He and / or Ne together with two or more gases selected from N ₂ , Ar, Kr and Xe. It is very preferable that the purge gas is He and / or Ne; Ar and / or N ₂ ; and Kr and / or Xe exists.

Usually, the purifying gas of He and / or Ne is of the order of 1 to 40, preferably 2 to 20, and more preferably 4 to 16, volume percent and two or more gases of N ₂ , Ar, Kr and Xe of the order of 60 to 99, preferably 80 to 98 and more preferably 84 to 96 volume percent have been selected. The purge gas may be, for example, He and / or Ne of the order of 2 to 20, preferably 4 to 16, percent by volume; Ar and / or N ₂ on the order of 50 to 96, preferably 60 to 92 percent by volume; and Kr or Xe are on the order of 2 to 40, preferably 3 to 30, percent by volume. It is best if the cleaning gas of He and / or Ne in the order of 2 to 20, preferably 4 to 16 volume percent; together with (i) Ar and / or N ₂ in the order of 50 to 70% by volume and Kr in the order of 10 to 40% by volume; or (ii) Ar and / or N _{2 is} on the order of 70 to 90% by volume and Xe is of the order of 0.5 to 20% by volume.

preferred Cleaning gases according to this embodiment include those listed in Table 2 below. All numbers are given in volume percent.

Table 2:

Embodiment 3

at the third embodiment of the invention, which is the same as the first embodiment except for described below, becomes a second harmonic interferometer for the setting the measurements of the interferometric displacement measuring means used, to account for temperature and pressure fluctuations. The second harmonic interferometer is above in embodiment 2 described. In this third embodiment, the reaction of the entire interferometric system adjusted to contaminants take into account by cleaning gas. This is achieved by the errors caused by contamination by cleaning gas have been added to each of the two interferometers.

wobei α_m1, α_m2 und α_m3 wie vorstehend definiert sind; und

wobei α_a1, α_a2 und α_a3 wie vorstehend definiert sind. Wie bei den Ausführungsformen 1 und 2 muss die Summe der Gasfraktionen gleich 1 sein, folglich ist

wobei F, j und k wie vorstehend definiert sind.In this embodiment, the purge gas consists of at least two components, and the following equation must be substantially satisfied:

wherein α _m1 , α _m2 and α _{m3 are} as defined above; and

wherein α _a1 , α _a2 and α _{a3 are} as defined above. As in Embodiments 1 and 2, the sum of the gas fractions must be 1, hence

where F, j and k are as defined above.

The refractive power of the cleaning gas for the wavelength λ ₁ is given by:

und für λ₃ durch:

mit der Bedingung, dass For the wavelength λ ₂ , the refractive power is given by:

and for λ ₃ by:

with the condition that

different Compositions of purge gas can be calculated by: equations (10), (11) and (12) are combined with the condition be satisfied that the equations (3), (4) and (5) are satisfied have to. For more information on refractive power, see, for example, Max Born & Emil Wolf, Principles of optics, electric theory of propagation interference and diffraction of light, sixth edition, Pergamon Press Oxford, which is hereby inserted by reference.

Suitable gas mixtures include mixtures of two or more components with different refractive powers. For example, the cleaning gas may include one or more components having a refractive power of less than 3 × 10 ^-4 at a wavelength of 200 to 700 nm or one or more components having a refractive power of more than 3 × 10 ^-4 at a wavelength of 200 to 700 nm , Usually, one or more components having a refractive power of less than 3 x 10 ^-4 at a wavelength of 200 to 700 nm are present in the order of 50 to 99 volume percent, and the one or more components having a refractive power greater than 3 x 10 ^-4 at a wavelength of 200 to 700 nm is present in the order of 1 to 50 percent by volume. The refractive index (or the refractive power) of the cleaning gas mixture at a wavelength λ ₁ differs from that of air when measured at the same wavelength, temperature and pressure.

For example, the purge gas may include two or more gases selected from N ₂ , He, Ne, Ar, Kr, and Xe. Usually, the purge gas consists of one or two gases selected from N ₂ , He, Ne and Ar together with Kr and / or Xe.

Usually, the purifying gas consists of N ₂ , He, Ne and / or Ar in the range of 50 to 99, preferably 65 to 98 volume percent and Kr and / or Xe in the order of 1 to 50, preferably 2 to 35 volume percent. The purifying gas may be, for example, N ₂ , He Ne and / or Ar in the order of 65 to 90% by volume and Kr in the order of 10 to 35% by volume. Alternatively, the purge gas may consist of N ₂ , He, Ne and / or Ar in the order of 90 to 98 volume percent and Xe in the order of 2 to 10 volume percent.

preferred Cleaning gases according to this embodiment include those listed in Table 3 below. All numbers are given in volume percent.

Table 3:

Embodiment 4

According to one another embodiment of the invention, which is the same as the first embodiment except for described below, a device can be used usually the effects due to temperature, pressure and contamination only partially compensated by cleaning gases. This embodiment can be particularly relevant if the cost or availability of certain components of the preferred cleaning gas, for Example Kr or Xe are intolerable.

at this embodiment can the correction coefficient K, by the second harmonic Interferometer has been determined to be optimized so that the Correction regarding pressure and temperature fluctuations not quite exactly, but that is due to the pollution with cleaning gas introduced errors are corrected to some extent. consequently will be a simultaneous correction of pressure, temperature and cleaning gas errors using an approximated Value of the second harmonic interferometer coefficient.

The approximate coefficient can be calculated as described below. In this calculation scheme, α _jx , α _mx, and α _{ax represent} the refractive power of a gas j, and the _purge gas and the air respectively represent the refractive power of air contaminated by a relative amount c of the _purge gas at a wavelength λ _x and α _cx . α cx = (1 - c) α ax + cα mx (13)

Both vortex flow and air contamination in the path of the interferometric displacement measuring means cause changes in the observed refractive index of the air in the measuring path. The error E in the measured distance is given by: E = (Δα c1 - KΔ (α c3 - a c2 )) L (14)

wobei p = p/T und Δρ die Änderung von ρ ist.Here, L is the length of the measuring path of the interferometric displacement measuring means, Δα _c1 is the change in refracting power at a wavelength λ _1, and Δ (α _c3 -α _c2 ) is the change in the refractive power difference between the wavelengths λ ₂ and λ _{3 of} the second harmonic interferometric system. The refractive powers are proportional to the quotient pressure (p) above the absolute temperature (T), so that only the pressure and temperature effects are taken into account, Δα _c1 and Δ (α _c3 - α _c2 ) are given by:

where p = p / T and Δρ is the change of ρ.

Taking into account the change in the relative magnitude of impurity contamination by the purge gas, Δc, Δα _c1 and Δ (α _c3 - α _c2 ) are given by: Δα c1 = Δc (α m1 - α a1 ) (17) Δ (α c3 - α c2 ) = Δc (α m3 - α a3 - α m2 + α a2 ) (18)

If σ _{ρ is} the standard deviation of ρ, then the deviation of the error due to vortex flow (σ _{E, ρ} ) is given by:

If σ _{c is} the standard deviation of c, then the standard deviation of the error due to contamination by the purge gas (σ _{E, ρ} ) is given by: σ E, c = σ c ((Α m1 - α a1 ) - K (α m3 - α m2 - α a3 + α a2 )) L (20)

The Gesamtveränderlichkeit the length measurement is given by:

Der daraus resultierende Optimalwert für K ist gegeben durch: The optimal value of K can be found by

The resulting optimal value for K is given by:

Of the The value of K given by this formula thus creates a simultaneous, though not necessarily complete, correction of pressure, Temperature and cleaning gas errors. If the variability the impurity is zero, the above formula is reduced on formula (5), i. those usually for correction only from Pressure and temperature is used.

The cleaning gas used in this embodiment may have a refractive index different from that of air at a wavelength λ ₁ . In another aspect of the embodiment, the cleaning gas has a refractive index at a wavelength λ ₁ equal to or substantially equal to that of air at the same wavelength, temperature and pressure.

Detecting is that the application of helium or neon alone, or predominantly alone, in this embodiment of the present invention possible is. Consequently, the purge gas may be at least 90%, preferably at least 95% or 98% either helium or neon alone or one Have mixtures of these gases. Both gases have a lot low refractive power and the change their refractive power between the wavelengths, generally used in lithographic interferometric devices equipment to be used is low. Contamination of the interferometric measuring range with one of these two gases acts effectively as if the pressure would have been reduced in the chamber, and this can be ordinary Be balanced by the second harmonic interferometer. The advantage of this aspect of the embodiment is that Helium and neon, especially helium, are relatively cheap gases. At the calculation an approximated one Coefficient K leads about that addition, the application of such a coefficient to a very small total error.

The However, combination of helium or neon with nitrogen creates one improved system that preserves the low overall error that Extent, to that generated by the two different interferometers Errors are added, but is much lower. this has the additional Advantage that small refractive errors in the two interferometers a smaller total error in that due to the interferometric System generated result. Therefore, there is an alternative Cleaning gas, which are used in this embodiment of the invention can, from a mixture of helium and / or neon with nitrogen. For example, a mixture of 90 to 99 volume percent nitrogen and 1 to 10 volume percent helium and / or neon or better 94 to 96 volume percent nitrogen and 4 to 6 volume percent helium and / or neon.

Even though in the foregoing special embodiments of the invention, it is clear that the invention can also be realized differently than described. The description is not intended to limit the invention.

Claims (28)

A lithographic projection apparatus comprising: an irradiation system for providing a projection beam of radiation; Patterning means for the pattern of the projection beam according to a desired pattern; a substrate table for holding a substrate; a projection system for imaging the patterned beam onto a target portion of the substrate, characterized by: interferometric displacement measuring means operating at a wavelength λ ₁ for measuring the position of the substrate table or the position of a table which is part of the patterning means; Purge gas means for supplying purge gas into a space to displace ambient air therefrom, the space receiving at least a portion of the substrate table and / or at least a portion of the table forming part of the pattern means, the purge gas for the projection beam of radiation substantially is non-absorbent and has a refractive index at a wavelength λ ₁ substantially equal to that of air when measured at the same wavelength, temperature and pressure; Gas supply means with the cleaning gas. An apparatus according to claim 1, wherein the cleaning gas has two or more components selected from N ₂ , He, AR, Kr, Ne and Xe. An apparatus according to claim 2, wherein the purge gas has at least 95 volume percent N ₂ and at least 1 volume percent Xe. An apparatus according to claim 2, wherein the cleaning gas at least 95% by volume of Ar and at least 1% by volume Xe has. An apparatus according to claim 2, wherein the cleaning gas at least 90% by volume of Ar and at least 5% by volume Kr has. An apparatus according to claim 2, wherein the purge gas has at least 95 volume percent N ₂ and at least 1 volume percent Ne. An apparatus according to claim 2, wherein the purge gas has at least 50 volume percent N ₂ and at least 35 volume percent Ar. An apparatus according to claim 2, wherein the purge gas has at least 94 volume percent N ₂ , at least 0.5 volume percent He and at least 0.5 volume percent Xe. An apparatus according to claim 1, further comprising a second harmonic interferometric measuring means operating at wavelengths λ ₂ and λ ₃ to adjust the measurements of the interferometric displacement measuring means to substantially eliminate effects of changes in pressure and temperature, and wherein the cleaning gas having three or more different constituents, each constituent having refractive values at the wavelengths λ ₂ and λ ₃ such that the following equations are substantially satisfied:

where F _{j is} the volume fraction of component j in the purge gas, the purge gas containing a total of k components; α _{j1 is} the refraction _value of the component j at a wavelength λ ₁ ; α _{j2 is} the refraction _value of the component j at a wavelength λ ₂ ; α _{j3 is} the refraction _value of the component j at a wavelength λ ₃ ; α _{a1 is} the refractive value of air at a wavelength λ ₂ ; and α _{a3 is} the refractive value of air at a wavelength λ ₃ ; and where

An apparatus according to claim 9, wherein the cleaning gas has three or more different components selected from N ₂ , He, Ar, Kr, Ne and Xe. An apparatus according to claim 10, wherein the purge gas comprises: (i) N ₂ and / or Ar in an amount of 50-90% by volume, (ii) Xe and / or Kr in an amount of 0.5 to 40% by volume and (iii ) He and / or Ne in an amount of 2 to 20% by volume. A lithographic projection apparatus comprising an irradiation system, patterning means, a substrate table and a projection system according to claim 1, characterized by: - an interferometric displacement measuring means as defined in claim 1; A second harmonic interferometric measuring means operating at wavelengths λ ₂ and λ ₃ for adjusting measurements of the interferometric displacement measuring means to substantially eliminate effects of changes in pressure and temperature; Purge gas means for supplying purge gas into a space to displace ambient air therefrom, the space receiving at least a portion of the sub strat and / or at least a portion of the table forming part of the pattern means, the purge gas for the projection beam of radiation in the Is substantially non-absorbent and has two or more constituents, each constituent having refractive indices at wavelengths λ ₁ , λ ₂ and λ ₃ such that the following equation is substantially satisfied:

where α _{m1 is} the refraction _{value of} the purge gas at a wavelength λ ₁ ; α _{m2 is} the refractive index of the cleaning gas at a wavelength λ ₂ ; α _{m3 is} the refraction _value of the cleaning gas at a wavelength λ ₃ and

where α _{m1 is} the refractive value of air at one of a wavelength λ ₁ ; and α _a2 and α _{a3 are} as defined in claim 9; and gas supply means comprising the purge gas. An apparatus according to claim 12, wherein the purge gas has two or more gases selected from N ₂ , He, Ar, Kr, Ne and Xe. An apparatus according to claim 13, wherein the purifying gas comprises: (i) N ₂ , He, Ar and / or Ne in an amount of 65 to 99.5% by volume and (ii) Kr and / or Xe in an amount of 0.5 to 35% by volume. A lithographic projection apparatus comprising an irradiation system, patterning means, a substrate table and a projection system as defined in claim 1, characterized by: purge gas means for supplying purge gas into a space to displace ambient air therefrom, the space at least part of the substrate table and / or or at least part of the table which is part of the patterning means, the cleaning gas for the projection beam of the radiation being substantially non-absorbent; An interferometric displacement measuring means as defined in claim 1; and - a second harmonic interferometric measuring means operating at wavelengths λ ₂ and λ ₃ for adjusting the measurements of the interferometric displacement measuring means (DI) according to the following equation: L = (DI) - K (SHI) (9) where L is the set measurement of the interferometric displacement measuring means, SHI is the measurement of the second harmonic interferometric measuring means, and K is a coefficient whose value is optimized so that effects of changes in pressure, temperature and cleaning gas composition are partially eliminated from the set measurement L in part , An apparatus according to claim 15, wherein the cleaning gas has a refractive index at a wavelength λ ₁ substantially equal to that of air measured at the same wavelength, temperature and pressure. An apparatus according to claim 15 or 16, wherein K is given by the equation:

where α _mx and α _{ax represent} the refractive value of the _{purge gas} and air at a wavelength λ _x, respectively, and α _{cx represents} the refractive value of air contaminated with a relative amount c of the purge gas at a wavelength λ _x , ρ a quotient term divided by represents the absolute temperature, σρ is the standard deviation of ρ and σ _{c is} the standard deviation of c. An apparatus according to any one of claims 15-17, wherein the purge gas has at least 95 volume percent He. An apparatus according to any of claims 15 to 17, wherein the purge gas has from 94 to 96 volume percent N ₂ and from 4 to 6 volume percent He. A device according to any one of the preceding claims, wherein λ _{1 is} approximately 633 nm, λ _{2 is} approximately 532 nm and λ _{3 is} approximately 266 nm. A device according to any one of the preceding claims, wherein the purge gas a supply of cleaning gas as defined in any one of the preceding claims, a gas flow regulator for controlling the flow rate of the cleaning gas in the room and suction for removal of the cleaning gas from the room. An apparatus according to claim 21, wherein the flow regulator a flow restrictor having. An apparatus according to claim 21 or 22, wherein the flow regulator a fan having. A device according to any one of the preceding claims, wherein the radiation of the projection beam has a wavelength of less than about 180 nm, preferably about 157 nm or 126 nm. A device manufacturing method comprising the steps of: a) providing a substrate which is at least partially covered by a layer of radiation-sensitive material; b) providing a projection beam of radiation using an irradiation system; c) using patterning means to pattern the projection beam in its cross-section; d) projecting the patterned beam of radiation onto a target area of the layer of radiation-sensitive material; e) determining the position of a table using interferometric displacement measuring means operating at a wavelength λ ₁ , the table being either suitable for holding the substrate or forming part of the patterning means; characterized by the step of - supplying cleaning gas into a space that accommodates at least a portion of the table to displace ambient air therefrom, the cleaning jet for the projection beam of radiation being substantially non-absorbent and having a refractive index at a wavelength λ ₁ , which is essentially the same as that of air, measured at the same wavelength, temperature and pressure. A method according to claim 25, further comprising the step of adjusting the measurement of the interferometric displacement measuring means to substantially eliminate effects of pressure and temperature variations using a second harmonic interferometric measuring means operating at wavelengths λ ₂ and λ ₃ is working; and wherein the cleaning gas has three or more different constituents, each constituent having refractive values at the wavelengths λ ₂ and λ ₃ such that the following equations are substantially satisfied:

wherein F _{j is} a volume fraction of the component j in the purge gas, the purge gas containing a total of k constituents; α _{j1 is} the refraction _value of the component j at a wavelength λ ₁ ; α _{j2 is} the refraction _value of the component j at a wavelength λ ₂ ; α _{j3 is} the refraction _value of the component j at a wavelength λ ₃ ; α _{a1 is} the refractive value of air at a wavelength λ ₁ ; α _{a2 is} the refractive value of air at a wavelength λ ₂ ; and α _{a3 is} the refractive value of air at a wavelength λ ₃ , and wherein:

A device manufacturing method comprising the steps a) to e) as defined in claim 25, characterized by the steps of: - adjusting the interferometric displacement measuring means to substantially eliminate the effects of changes in pressure and temperature, wherein a second harmonic interferometric Measuring means is used which operates at wavelengths λ ₂ and λ ₂ ; Supplying purge gas into a space having at least a portion of the table to displace ambient air therefrom, the scrubbing gas for the projection beam of radiation being substantially non-absorbent and having two or more constituents, each constituent having refractive values at the wavelengths λ ₁ , λ ₂ and λ ₃ such that the following equation is substantially satisfied:

where α _{m1 is} the refraction _{value of} the purge gas at a wavelength λ ₁ ; α _{m2 is} the refractive index of the cleaning gas at a wavelength λ ₂ ; am3 is the refractive index of the cleaning gas at a wavelength λ ₃ ; and

where α _{a1 is} the refractive index of air at a wavelength λ ₁ ; α _{a2 is} the refractive index of air at a wavelength λ ₂ ; and α _{a3 is} the refractive index of air at a wavelength λ ₃ . A device manufacturing method comprising the steps a) to d) as defined in claim 25, characterized by the steps of: supplying cleaning gas to a space receiving at least a portion of a table to displace ambient air therefrom, the table being either suitable is formed to hold the substrate or a part of the patterning means, wherein the cleaning gas for the projection beam from the radiation is substantially non-absorbing; Determining the position of the table using an interferometric displacement measuring means operating at a wavelength λ ₁ ; and adjusting the measurement of the interferometric displacement measuring means (DI) using a second harmonic interferometric measuring means operating at wavelengths λ ₂ and λ ₃ according to the following equation: L = (DI) - K (SHI) (9) where L is the set interferometric displacement measurement measurement, SHI is the second harmonic interferometric measurement means measurement, and K is a coefficient whose value is optimized to partially eliminate the effects of changes in pressure, temperature, and purge gas composition from the set value L. ,