JP2002110538A - Lithographic projector, method for manufacturing device, device manufactured thereby and gas composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithographic projector using two or more color interferometer devices by an arbitrary selection to accurately obtain a position of a movable table in the projector. SOLUTION: The lithographic projector comprises a flushing gas means for supplying a purge gas to a space for housing at least a part of the movable table. In this case, the purge gas is selected so that a leakage of the purge gas into an operating area of the interferometer device may not bring about a significant error of an interferometer measured value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a radiation system for providing a projection beam of radiation, a patterning means for patterning the projection beam according to a desired pattern, a substrate table for holding a substrate, and a patterning device. A projection system for imaging the shaped beam onto a target portion of the substrate.

[0002]

BACKGROUND OF THE INVENTION The term "patterning means" is to be interpreted broadly as referring to means that can be used to impart a pattern of cross-section to an incoming radiation beam corresponding to the pattern to be formed on a target portion of a substrate. Should. The term "light valve" can also be used in this context. Generally, the said pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). Examples of such patterning means include the following. A mask table for holding the mask. The concept of a mask is well known in lithography and includes mask types such as two-phase, AC phase shift, attenuated phase shift, as well as various hybrid mask types. Placing such a mask in the beam of radiation results in selective transmission (for a transmissive mask) or reflection (for a reflective mask) of radiation impinging on the mask, depending on the pattern on the mask. The mask table ensures that the mask can be held in a desired position in the incoming radiation beam, and that the mask can be moved relative to the beam if desired. A programmable mirror array. One example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such a device is:
For example, addressed areas of the reflective surface reflect incident light as diffracted light, and unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the undiffracted light can be filtered out of the reflected beam, leaving only the diffracted 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 suitable electronic means. More information on such mirror arrays can be gleaned, for example, from US Pat. Nos. 5,296,891 and 5,523,193, which are incorporated herein by reference.
A programmable LCD array. One example of such a configuration is described in US Pat.
872. For the sake of simplicity, the remainder of this text will focus in particular on examples involving mask tables and masks in several places. However, the general principles discussed in such examples should be seen in the broader context of the patterning means described herein above.

[0003] Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning means can generate a circuit pattern corresponding to the individual layers of the IC, and place this pattern on a substrate (silicon wafer) that is covered with a layer of radiation-sensitive material (resist). (E.g., comprising one or more dies).
In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. Current equipment employing patterning by a mask on a mask table can be divided into two different types of machines. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion at once. Such equipment is generally
Called stepper. In an alternative device (commonly referred to as a step-and-scan device), each target portion is
Illumination is achieved by progressively scanning the mask pattern under the projection beam in a given reference direction (the "scan" direction) while simultaneously scanning the substrate table parallel to this direction or antiparallel. Generally, since the projection system has a magnification factor M (typically <1), the speed V at which the substrate table is scanned will be M times the speed at which the mask table is scanned. More information regarding the lithographic devices described herein can be gleaned, for example, from US Pat. No. 6,046,792, which is incorporated herein by reference.

In a manufacturing process using a lithographic projection apparatus, a pattern (eg, with a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging step, priming, resist coating, soft coating
Various treatments such as baking can be performed. After exposure,
Other treatments may be applied to the substrate, such as post-exposure bake (PEB), development, hard bake, and measurement / inspection of the imaged features. This series of actions involves the device,
Used, for example, as a basis for patterning individual layers of an IC. The patterned layer can then be subjected to various processes such as etching, ion implantation (doping), metallization, oxidation, chemical mechanical polishing, and the like. These are all for completing the individual layers. If multiple layers are required, the entire procedure, or a variant thereof, must be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices can then be separated from one another by techniques such as dicing and sawing, and the individual devices can be attached to carriers, for example, or connected to pins. Further information on such processes can be found, for example, in Peter van Zant, which is incorporated herein by reference.
"Microchip Fabricatio
n: A Practical Guide to Se
microcomputer Processing ", T
third Edition, McGraw Hill
Publishing Co. , 1997, ISBN0
-07-067250-4.

[0005] For simplicity, the projection system may hereinafter be referred to as a "lens". But,
This term should be interpreted broadly to encompass various types of projection systems, including, for example, refractive optics, catoptric optics, catadioptric optics. The radiation system can also include components that operate according to any of these design types for directing, shaping, or controlling a projected beam of radiation, and such components are also collectively referred to below. , Or individually referred to as a “lens”. Further, the lithographic apparatus may be of a type having two or more substrate tables (and / or two or more mask tables). In such a "multi-stage" device, additional tables can be used in parallel, or preparatory steps can be performed on one or more tables while exposing one or more other tables. it can. A two-stage lithographic apparatus is described, for example, in US Pat. No. 5,969,961, which is incorporated herein by reference.
No. 441 and WO 98/40791.

[0006] In order to reduce the size of features that can be imaged, it is desirable to reduce the wavelength of the illumination radiation. Therefore, less than 180 nm, for example 157n
A wavelength of m or 126 nm is employed. However, such wavelengths are strongly absorbed by the normal atmosphere as the beam traverses the device, resulting in unacceptable loss of intensity. To solve this problem, it has long been proposed to flow a gas stream through the device, the gas being substantially transparent to the illumination wavelength, for example nitrogen (N ₂ ).

[0007] The lithographic projection apparatus can be provided with an interference displacement measurement means, which is used to accurately determine the position of a movable table, such as a mask or a substrate table. This means uses a measuring beam of coherent monochromatic radiation to measure the optical path length (geometric distance x refractive index) to the movable table. The measuring means is very sensitive to changes in pressure and temperature, as well as changes in the composition of the medium traversed by the measuring beam. All three of these variables affect the refractive index of the medium. Typically, a second harmonic interference device is used to allow for refractive index changes caused by temperature and pressure fluctuations. More information on such a second harmonic interference device that can compensate for temperature and pressure fluctuations can be found, for example, in US Pat. No. 5,404,222, which is incorporated herein by reference.

[0008] Alternatively, the second harmonic interferometer can compensate for changes in the composition of the medium. However, this second interferometer device cannot simultaneously observe changes in pressure and temperature and changes in the composition of the medium.

A purge gas can be flowed through some space in the projection apparatus to remove any gas, such as oxygen or water, that absorbs radiation at the wavelength of the projection beam of radiation.
The inventor has noted that if the gas used to purge the system enters the areas where the interference displacement measurement means operate, the refractive index in those areas will change and affect the position measurements. Was found. Changes in the refractive index of the medium must be avoided so that the measuring means continues to operate with the required high accuracy.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lithographic projection apparatus in which the outflow of purge gas does not affect the interference displacement measuring means.

[0011]

According to the present invention, there is provided, in accordance with the present invention, a method for operating at a wavelength λ ₁ for measuring the position of the substrate table or of a table which is part of the patterning means. Interfering displacement measuring means, and flushing gas means for supplying a purge gas to the space to expel the atmosphere from the space, wherein the space comprises at least a portion of the substrate table and / or the patterning. Means for accommodating at least a portion of the table being part of the means, wherein the purge gas does not substantially absorb the projection beam of radiation and is measured at the same wavelength, temperature, and pressure. The lithographic apparatus specified in the opening paragraph is characterized by having a refractive index substantially equal to that of air at wavelength λ ₁ .

The present inventor has proposed that, for example, by flowing a specific gas composition having the same refractive index as air under the same measurement conditions, through a mask stage and a substrate stage, each of which usually has a movable mask and a substrate table, respectively, the It has been found that the measuring means can operate with the required precision, while allowing the use of radiation with a wavelength of 180 nm or less.

According to a further embodiment of the present invention, furthermore, operating at wavelengths λ ₂ and λ ₃ for adjusting the measurements of said interference displacement measuring means so as to substantially eliminate the effects of pressure and temperature changes. A second harmonic interference measuring means, wherein the purge gas contains three or more different components,
Each component is an equation

(Equation 12)

(Equation 13) Where F _j is the refractive index at wavelengths λ ₂ and λ ₃ , wherein F _j is the volume of component j in the purge gas containing a total of k components. Percentage,
α _j1 is the refractive index of component j at wavelength λ ₁ , α _j2 is the refractive index of component j at wavelength λ ₂ , α _j3 is the refractive index of component j at wavelength λ ₃ , α _a1 is the refractivity of air at a wavelength λ _1, α _a2 is the refractivity of air at a wavelength λ _2, α _a3 is the refractivity of air at a wavelength lambda _3,

[Equation 14] The specified device is provided.

If a second harmonic interferometer is present in the system, simply adjusting the refractive index of the purge gas relative to the refractive index of air at the wavelength at which the displacement measuring interferometer operates will result in a purge gas leak. Is not enough to overcome the error in the displacement measurement caused by the Thus, the inventor typically has at least three different refractive indices, each having a significantly different refractive index.
A purge gas composition containing two different components was devised (where the refractive index is defined as refractive index-1). By properly selecting the gas so that the gas satisfies or substantially satisfies the equation given above, the compositional change of the purge gas is such that, for any interferometer measurement, Or has little effect. Thus, accurate position measurements can be obtained that take into account changes in temperature, pressure, and purge gas leakage.

According to a further aspect of the invention, there is provided an interference displacement measuring means operating at a wavelength λ ₁ for measuring the position of the substrate table or of a table which is part of the patterning means; A second harmonic interference measuring means operating at wavelengths λ ₂ and λ ₃ for adjusting the measurements of said interference displacement measuring means to substantially eliminate the effects of changes, and to expel the atmosphere from space, Flushing gas means for supplying a purge gas to the space, wherein the space houses at least a part of the substrate table and / or at least a part of the table which is a part of the patterning means. Means, wherein the purge gas does not substantially absorb the projected beam of radiation and comprises two or more components, each component having the equation

(Equation 15) _Where α _m1 is the refractive index of the purge gas at wavelength λ ₁ , and α _m2 has a refractive index at wavelengths λ ₁ , λ ₂ , and λ ₃ that substantially satisfies is the refractivity of the purge gas at a wavelength λ _2, α _m3 is the refractivity of the purge gas at a wavelength lambda _3,

(Equation 16) Where α _a1 is the refractive index of air at wavelength λ ₁ , α _a2 is the refractive index of air at wavelength λ ₂ , and α _a3 is the refractive index of air at wavelength λ ₃ The lithographic apparatus specified in the opening paragraph is provided.

In this embodiment, neither the displacement measurement interferometer nor the second harmonic interferometer need provide an accurate measurement taking into account purge gas contamination. Rather, this aspect ensures that the entire interferometer system is adjusted to allow for the effects of purge gas contamination. This is achieved by canceling the error of the displacement measuring interferometer with the error of the second harmonic interferometer. This aspect of the invention provides an alternative way in which the effects of temperature, pressure, and purge gas leaks can be accurately accounted for in the interferometer readings, providing a simpler gas mixture, e.g., only two different It allows to use a mixture of gases.

According to a further aspect of the present invention, there is provided a flushing gas means for supplying a purge gas to the space to expel the atmosphere from the space, wherein the space includes at least a part of the substrate table. And / or means for accommodating at least a portion of a table that is part of the patterning means, wherein the purge gas does not substantially absorb the projection beam of radiation, and An interference displacement measuring means operating at a wavelength λ ₁ for measuring the position of the table, which is part thereof, and the equation L = (DI) −K (SHI)
A second harmonic interference measuring means operating at wavelengths λ ₂ and λ ₃ for adjusting the measured value (DI) of said interference displacement measuring means according to (9), wherein:
L is the measured value of the interference displacement measuring means after the adjustment, and SHI
Is the measured value of the second harmonic interference measuring means, and K is a coefficient whose value is partially different from the adjusted measured value L from the effects of changes in pressure, temperature and purge gas composition. There is provided a lithographic apparatus as specified in the opening paragraph, characterized in that the lithographic apparatus is optimized for:

In this aspect of the invention, coefficient K is optimized such that the possible error in length measurement L is minimized. This embodiment is less demanding than the first three embodiments of the present invention with respect to the particular combination of gases that can be used, and thus can reduce the errors introduced by purge gas composition changes. Offers a higher style.

According to a further aspect of the present invention, providing a substrate at least partially covered by a layer of radiation-sensitive material, providing a projection beam of radiation using a radiation system, and patterning means. use, a and providing a pattern in its cross-section to the projection beam, a device manufacturing method comprising the steps of: projecting the patterned radiation beam onto a target area of the layer of radiation-sensitive material, the wavelength lambda ₁ Determining the position of the table using interference displacement measurement means operating in the step, wherein the table is suitable for holding the substrate or forming part of the patterning means; and Providing a purge gas to a space containing at least a portion of Wherein the purge gas does not substantially absorb the projection beam of radiation and has the same wavelength, temperature,
And having a refractive index at wavelength λ ₁ that is substantially the same as the refractive index of air when measured at and pressure.

In one preferred embodiment, the method further comprises using second harmonic interferometers operating at wavelengths λ ₂ and λ ₃ to substantially eliminate the effects of pressure and temperature changes. Adjusting the measured value of the interference displacement measuring means. In this embodiment, the purge gas includes three or more different components, each component having the equation

[Equation 17]

(Equation 18) Where F _j is the refractive index at wavelengths λ ₂ and λ ₃ , wherein F _j is the volume of component j in the purge gas containing a total of k components. Percentage,
α _j1 is the refractive index of component j at wavelength λ ₁ , α _j2 is the refractive index of component j at wavelength λ ₂ , α _j3 is the refractive index of component j at wavelength λ ₃ , α _a1 is the refractivity of air at a wavelength λ _1, α _a2 is the refractivity of air at a wavelength λ _2, α _a3 is the refractivity of air at a wavelength lambda _3,

[Equation 19] It has become.

A further aspect of the invention is to provide a substrate at least partially covered by a layer of radiation-sensitive material, to provide a projection beam of radiation using a radiation system, and to use patterning means. Providing a projection beam with a pattern in its cross-section, and projecting the patterned radiation beam onto a target area of a layer of radiation-sensitive material, the method operating at wavelength λ ₁ . a step for determining the position of the table using interferometric displacement measuring means for the steps of the table are suitable for forming a part of the holding to, or the patterning means the substrate, the wavelength lambda ₂ and lambda ₃ prior to substantially eliminate the effects of changes in pressure and temperature using a second harmonic interferometric measuring means operating at Adjusting the measured value of the interference displacement measuring means; and providing a purge gas to a space containing at least a portion of the table to expel air therefrom, wherein the purge gas comprises Does not substantially absorb the projection beam, and comprises two or more components, each component having the equation

(Equation 20) _Where α _m1 is the refractive index of the purge gas at wavelength λ ₁ , and α _m2 has a refractive index at wavelengths λ ₁ , λ ₂ , and λ ₃ that substantially satisfies is the refractivity of the purge gas at a wavelength lambda _2, alpha _m3 is the refractivity of the purge gas at a wavelength lambda _3,

(Equation 21) Where α _a1 is the refractive index of air at wavelength λ ₁ , α _a2 is the refractive index of air at wavelength λ ₂ , and α _a3 is the refractive index of air at wavelength λ ₃ A method is provided.

A further aspect of the invention is to provide a substrate at least partially covered by a layer of radiation-sensitive material, to provide a projection beam of radiation using a radiation system, and to use patterning means. Providing the projection beam with a pattern in its cross-section, and projecting the patterned beam of radiation onto a target area of a layer of radiation-sensitive material, the device comprising: Providing a purge gas to a space containing the gas and expelling air therefrom, wherein the table is suitable for holding the substrate or forming part of the patterning means, The gas does not substantially absorb the projection beam of radiation, and the wavelength λ
Determining the position of said table using the interference displacement measuring means operating at _1; a second key operating at wavelengths λ ₂ and λ ₃ according to the equation L = (DI) -K (SHI) (9) Using the wave interference measuring means, the measured value (D
Adjusting I), wherein in said equation:
L is the measured value of the interference displacement measuring means after the adjustment, and SHI
Is the value measured by the second harmonic interference measuring means, K is a coefficient, the value of which is partially eliminated from the adjusted value L by the effects of changes in pressure, temperature, and purge gas composition. And a step that is optimized to:

Although particular reference may be made in this text to the use of devices according to the present invention in IC manufacture, it should be clearly understood that such devices also have many other possible applications. For example, it can be used for manufacturing integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, and the like. In the context of such alternative applications, the terms "reticle" in this text,
Those skilled in the art will appreciate that the use of "wafer" or "die" should be considered as being replaced by the more general terms "mask", "substrate", and "target area", respectively.

In this document, the terms "illumination radiation" and "illumination beam" are referred to as ultraviolet radiation (eg, wavelengths 365, 2,
48, 193, 157, or 126 nm), and E
It is used to encompass UV and all types of electromagnetic radiation, including particle beams such as ion beams and electron beams.

Next, embodiments of the present invention will be described by way of example only with reference to the accompanying schematic drawings.

In the figures, corresponding reference numerals indicate corresponding parts.

[0027]

FIG. 1 schematically illustrates a lithographic projection apparatus according to one particular embodiment of the invention. This device comprises: Radiation (eg UV or EUV radiation, eg less than 180 nm,
A radiation system L for supplying a projection beam PB (e.g. radiation having a wavelength of about 157 nm or 126 nm).
A, Ex, IL. A first object table (mask table) MT comprising a mask holder for holding a mask MA (eg a reticle) and connected to first positioning means for accurately positioning the mask with respect to the item PL. . Item PL including a substrate holder for holding a substrate W (for example, a resist-coated silicon wafer)
A second object table (substrate table) WT connected to second positioning means for accurately positioning the substrate with respect to. A projection system ("lens") PL (e.g., a refractive or catadioptric system of mirrors) for imaging an illuminated portion of the mask MA onto a target portion C (comprising one or more dies) of the substrate W.

As shown herein, the apparatus is of a transmissive type (ie, has a transmissive mask). However, in general, for example, it may be of a reflective type (having a reflective mask). Alternatively, the device may be a programmable mirror of the type mentioned above.
Other types of patterning means, such as an array, can be used.

The radiation system includes a radiation source LA (eg, an Hg lamp or an excimer laser) that produces a beam of radiation. This beam is fed to an illumination system (illuminator) IL, either directly or after having passed through conditioning means, such as a beam expander Ex, for example. The illuminator IL is
It comprises adjusting means AM for setting the outer and / or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution of the beam. Further, various other components such as an integrator IN and a condenser lens CO are generally provided. In this way, the beam PB impinging on the mask MA has the desired uniformity and intensity distribution in its cross section.

Referring to FIG. 1, the source LA may be inside the housing of the lithographic projection apparatus (eg, as is often the case when the source LA is a mercury lamp), but is remote from the lithographic projection apparatus. Note that the resulting radiation beam may be directed into the device (eg, by a suitable directing mirror). This latter scenario is often the case when the source LA is an excimer laser. The current invention and claims encompass both of these scenarios.

The beam PB then intersects the mask MA, which is held on the mask table MT in the mask holder. After traversing the mask MA, the beam PB passes through a lens PL, which focuses the beam PB on a target portion C of the substrate W. The second positioning means (and the interferometer measuring means IF with an interferometric displacement measuring device operating at a wavelength λ ₁ , for example at about 633 nm) positions the substrate table WT, for example in the path of the beam PB, of the various target parts C. You can move exactly as you do. Similarly, the first positioning means can be used to accurately position the mask MA with respect to the path of the beam PB, for example after a mechanical search for the mask MA from a mask library or during a scan. In general, the movement of the object tables MT, WT is realized using a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), not explicitly shown in FIG. However, in the case of a wafer stepper (unlike a step and scan device)
The mask table MT can be connected to a short-stroke actuator only, or can be fixed.

The illustrated device can be used in two different modes. 1. In the step mode, the mask table MT is kept essentially stationary, and the entire mask image is projected onto the target portion C at one time (ie with only one "flash"). Then, the substrate table WT is shifted in the x and / or y direction, so that another target portion C can be irradiated by the beam PB. 2. In scan mode, essentially the same scenario applies, except that a given target portion C is not exposed in a single "flash". 1
Rather than exposing in a single flash, the mask table MT can be moved in a given direction (the so-called "scan direction", e.g. the x-direction) at a speed v so that the projection beam PB scans over the mask image It is supposed to. At the same time, the substrate table WT
Are simultaneously moved in the same or opposite directions at a speed V = Mv. Here, M is the magnification of the lens PL (typically, M = 1/4 or 1/5). In this manner, a relatively large target portion C can be exposed without deteriorating the resolution.

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

The mask M is held in the concave portion of the mask table MT, and the mask table MT is
It can be seen that it can be manufactured from a ceramic material such as (RTM) and is positioned by a drive system (not shown) during operation of the lithographic apparatus. The mask table MT is the last element of the collimating optics CO that produces the projection beam PB and the projection lens that projects the projection beam PB that has passed through the mask M onto the wafer W (shown in FIGS. 1 and 3). It is sandwiched in close proximity to the first element of the system PL.

The mask steps are defined in the following zones or spaces 2-6:
Can be divided into The space 2 is between the final illuminator optics CO and the mask table MT. Space 3 is
Inside the mask table MT, above the mask M.
The space 4 is between the mask M and the thin film 13 inside the mask table MT. Space 5 is a mask table MT
Inside, below the membrane 13. The space 6 is between the mask table MT and the projection lens system PL. Each space is provided by a corresponding one of the flow regulators 112 to 11 from the gas supply source 11.
The purge gas provided through 6 is flushed. On another side of each space, the purge gas is supplied to the respective vacuum pump 122
Through 126 to the reservoir 12. The reservoir 12 can be partitioned to control and reuse the gas in the selected space, and the device 1 can be used to clean or scrub the recovered gas.
2a.

If desired, the various spaces in the mask step can be separated from one another to ensure laminar flow. For example, a thin sheet 14 such as CaF or dissolved SiO ₂
To cover the recesses of the mask table MT,
The space 2 can be separated from the space 3. Similarly, sheets 15 and 16 can be used to separate the spaces 5 and 6 and cover the non-planar surface of the first element of the projection lens system PL, respectively.

In the mask table MT, spaces 3, 4,.
Appropriate conduits are provided in the body of the mask table to supply and remove gas flows to and from the mask table. When the mask table has been exposed to air, for example, after a period of non-operation of the apparatus or after changing the mask, a purge gas is supplied for a short time before the exposure is performed, for example, to deposit on an uneven portion of the mask table. Drain out any air you may have.

FIG. 3 shows a wafer stage of the lithographic apparatus of FIG. To avoid having to provide a purge gas path that covers the entire range of movement of the wafer stage,
The gas supply outlet 17 and the exhaust inlet 18 are connected to the projection lens system P
The lower end of L is attached to each side of the final element. The outlet 17 and the inlet 18 are connected to the gas supply source 11 and the reservoir 12 via the flow regulator 117 and the vacuum pump 127, respectively. Especially exit 17, but entrance 1
8 can also be provided with vanes to guide the flow of the purge gas. If not already flat, the final element of the projection lens system PL can be covered by the thin sheet described above.

The flow regulators 112-117 described above provide the static or controllable pressure or flow reducers and / or blowers required to provide the required gas flow for the particular embodiment and available gas supply. Can be prepared.

According to the invention, the mask stage of the apparatus and / or
Alternatively, a purge gas can flow through the substrate stage. Purge gas comprises _{typically, N 2, He, Ne,} Ar, Kr, and mixtures of two or more gases selected from Xe. The gas composition used is substantially transparent to the projection beam at the UV radiation wavelength, and when measured using the same wavelength radiation under the same temperature and pressure conditions (eg, standard clean room conditions), It has substantially the same refractive index as air. The refractive index should be the same as the refractive index of air at the wavelength of the radiation beam used in the interference displacement measuring means IF. The pressure of the purge gas at the mask stage and / or substrate stage may be at or above atmospheric pressure, so that any leaks will cause a gas bleed and the incoming air will cause the system to Not contaminated.

To determine a gas mixture suitable for use 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 particular partial pressure, temperature, and wavelength λ ₁ can be determined using the following equation:

(Equation 22) Here, n _j1 is the refractive index of the purge gas j at the wavelength λ ₁ .

The refractive index α is calculated by the following equation.
Has to do with. α _i = n _i −1 (6a) Thus, for a mixture of k gases,

(Equation 23) Where F _j is the relative volume concentration of gas j and α
_j1 is the refractivity of the purge gas j at a wavelength lambda _1. Thus, for this embodiment of the invention, if the purge gas consists of a 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 (8) where α _a1 is the refractive index of air at the wavelength λ ₁ . Or, more generally,

(Equation 24) Where F _j , α _j1 , and α _a1 are as defined above,

(Equation 25) Becomes

The index of refraction and the index of refraction are dependent on pressure, temperature, and wavelength, so that the values of n and α in the above equations, and in all other equations described herein, are the same for both temperature and temperature. Must be related to pressure. Normally, standard clean room conditions are used. The wavelength λ ₁ used for this calculation should be the same as at least one wavelength of the radiation beam of the interference displacement measuring means.

Suitable gas mixtures that fit this equation include N ₂ and 1-5% by volume of He, preferably 2-3% by volume of He, 1-5% by volume of Ne, preferably 3. 5-
2.5 vol% Ne, or 35-50 vol% Ar,
A mixture comprising preferably 40 to 45% by volume of Ar,
a mixture comprising r and 1-5% by volume of Xe, preferably 2-3% by volume of Xe, Ar and 5-10% by volume of Kr,
Mixture preferably comprising a 6-8% by volume of Kr, and the N _2, and 0.5 to 3% by volume the He, 0.5-3 vol%
And a mixture containing Xe. Λ wavelength of 633 nm
Preferred gas mixtures for use in _1, Table 1 below
Are included. All figures are in volume%.

[Table 1]

(Embodiment 2) In this embodiment of the present invention, which is the same as the first embodiment except as described below,
The interferometer measuring means IF includes an interference displacement measuring device and a second
And a harmonic interference device. A second harmonic interference device measures the refractive index of the atmosphere in the device at two different wavelengths. In this way, it is possible to determine the effect of pressure and temperature on the refractive index and adjust the displacement interferometer measurements in view of such changes accordingly.

[0046] This measurement value of the second harmonic interferometer is multiplied by the coefficient K _a, then, is accomplished by subtracting this value from the displacement interferometer measurement. Therefore, the corrected length L
Is given by L = (DI) −K _a (SHI) (9) Where DI is the displacement interferometer measurement, SHI is the second harmonic interferometer measurement, and DI
And SHI are corrected for operation in average air.

The coefficient K _a is determined from the following equation.

(Equation 26) Where α _ay is the refraction of air at wavelength λ _y , the interference displacement measuring means is operated at wavelength λ ₁ , the second harmonic interferometer measuring means is operated at wavelengths λ ₂ and λ ₃ , Wavelength λ ₂ is typically larger than wavelength λ ₃ . For example, λ ₂ is about 532 nm and λ ₃ is about 266 nm. Usually, λ ₁ is different from λ ₂ and λ ₃ . However, it is also possible for λ ₁ to be equal to λ ₂ or λ ₃ .

Adjustment of the displacement interferometer measurements in this manner ensures that the position measurements are not affected by changes in temperature and pressure inside the lithographic apparatus.

By selecting a purge gas having the same refractive index (or refractive index) as air at wavelength λ ₁ , the displacement interferometer device is accurate even when the purge gas leaks into the measurement area. Is guaranteed. However, leakage of the purge gas still results in large inaccuracies in refractive index measurements at wavelengths λ ₂ and λ ₃ at which the second harmonic interferometer operates. This can lead to errors in the final position measurement. This embodiment of the present invention addresses this problem by ensuring that purge gas leaks do not affect either interferometer device. This can be achieved by using a purge gas containing three or more k gases and satisfying or substantially satisfying the following three equations:

[Equation 27]

[Equation 28]

(Equation 29) Here, F, α, j, and k are as defined above.

By simultaneously solving the above three equations, the required ratio of each gas j can be determined. Satisfying equation (1) ensures that the refractive index (or refractive index) of the mixture at wavelength λ ₁ will be the same as 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 having different refractive indices. For example, if the purge gas is 200-700
one or more components having a refractive index of less than 1 × 10 ^{−4 at} a wavelength of nm and 1 × 1 at a wavelength of 200-700 nm;
And two or more components having a refractive index greater than 0 ^-4 . Usually, a component having a refractive index of less than 1 × 10 ^-4 at a wavelength of 200 to 700 nm contains 1 to 40% by volume, preferably 2
Two or more components present in an amount of ２０20% by volume and having a refractive index of greater than 1 × 10 ^-4 at a wavelength of 200-700 nm are 60-99% by volume, preferably 80-98% by volume.
Exists in the amount of

For example, the purge gas may be N ₂ , He, N
It may include three or more gases selected from e, Ar, Kr, and Xe. Typically, the purge gas is He
And / or Ne by N ₂ , Ar, Kr, and Xe
And two or more gases selected from the group consisting of: More preferably, the purge gas comprises He and / or Ne;
It contains Ar and / or N ₂ and Kr and / or Xe.

Usually, the purge gas is 1 to 40% by volume,
Preferably He and / or Ne in an amount of 2-20% by volume, more preferably 4-16% by volume, and 60-99% by volume, preferably 80-98% by volume, more preferably 84% by volume.
96 vol% of the amount of N _2, includes Ar, Kr, and the two or more gases selected from Xe. For example, 2-20
% By volume, preferably 4-16% by volume of He and / or
Or, Ne and 50 to 96% by volume, preferably 60 to 9% by volume.
Ar and / or N2 in an amount of ₂ % by volume and Kr or Xe in an amount of ₂ to 40% by volume, preferably 3 to 30% by volume.
And More preferably, He and / or Ne in an amount of 2-20% by volume, preferably 4-16% by volume,
(I) of 50 to 70 volume% of the amount Ar and / or N ₂
And Kr in an amount of 10 to 40% by volume, or (i
i) Ar and / or N in an amount of 70-90% by volume
₂ and Xe in an amount of 0.5 to 20% by volume.

Preferred purge gases according to this embodiment include those described in Table 2 below. All figures are given in volume%.

[Table 2]

Embodiment 3 A third embodiment of the present invention, which is the same as the first embodiment except as described below, uses a second harmonic interference device to reduce the temperature and pressure. Adjust the measured value of the displacement interferometer in anticipation of the change. The second harmonic interference device has been described in the second embodiment.
In this third embodiment, the response of the entire interferometer system is adjusted to allow for purge gas contamination. This is 2
It is achieved by canceling errors caused by purge gas contamination in each of the two interferometer devices.

In this embodiment, at least two components make up the purge gas and must substantially satisfy the following equation:

[Equation 30] Where α _m1 , α _m2 , and α _m3 are as defined above,

(Equation 31) And α _a1 , α _a2 , and α _a3 are as defined above. As in the case of Embodiments 1 and 2, the sum of the gas proportions is 1, that is,

(Equation 32) Where F, j, and k are as defined above.

The refractive index of the purge gas at the wavelength λ ₁ is

[Equation 33] Given by In the wavelength lambda _2, the refraction is

(Equation 34) And at λ ₃

(Equation 35) And

[Equation 36] There is a condition.

On the condition that equations (3), (4) and (5) must be satisfied, equations (10), (1)
By combining 1) and (12), various purge gas compositions can be calculated. For more information on refractive index, see, for example, Max Born & EmilW, which is incorporated herein by reference.
Olf, "Principles of optic"
s, electric theory of pro
pagination interference
difference of light ", six
the edition, Pergamon Press
See Oxford.

[0059] Suitable gas mixtures include mixtures of two or more components having different indices of refraction. For example, the purge gas comprises one or more components having a refractive index of less than 3 × 10 ⁻⁴ at a wavelength of 200-700 nm,
It contains one or more components having a refractive index greater than 3 × 10 ^{−4 at} wavelengths of 700 nm. Usually 200 ~
1 having a refractive index of less than 3 × 10 ^-4 at a wavelength of 700 nm
The component or components are present in an amount of 50 to 99% by volume, and the component or components having a refractive index of greater than 3 × 10 ^-4 at a wavelength of 200 to 700 nm are present in an amount of 1 to 50% by volume. Exist in quantity. The refractive index (or refractive index) of the purge gas mixture at wavelength λ ₁ differs from air when measured at the same wavelength, temperature, and pressure.

For example, the purge gas may be N ₂ , He, N
It can include two or more gases selected from e, Ar, Kr, and Xe. The purge gas is typically N ₂ ,
It contains one or more gases selected from He, Ne, and Ar, and Kr and / or Xe.

[0061] Usually, the purge gas is 50 to 99 vol%, preferably 65 to 98% by volume of the amount of N _2, the He, N
e and / or Ar and Kr and / or Xe in an amount of 1-50% by volume, preferably 2-35% by volume. For example, 65 to 90 vol% of the amount of N _2, the He, N
e and / or Ar and K in an amount of 10 to 35% by volume
r. Alternatively, 90 to 98% of the amount of N _2, H
e, Ne, and / or Ar and Xe in an amount of 2-10% by volume.

[0062] Preferred purge gases according to this embodiment include those described in Table 3 below. All figures are given in volume%.

[Table 3]

Embodiment 4 According to a further embodiment of the present invention which is the same as the first embodiment except as described below, typically the effects of temperature, pressure and purge gas contamination Can be used to compensate only partially. This embodiment may be particularly important where the cost or availability of certain components of the preferred purge gas, such as Kr and Xe, is limited.

In this embodiment, the correction coefficient K obtained by the second harmonic interference device is not so accurately corrected in consideration of pressure and temperature changes, but the error introduced by contamination by the purge gas is corrected to some extent. Can be optimized. Therefore, simultaneous correction of pressure, temperature, and purge gas errors using the appropriate value of the second harmonic interferometer coefficient is used.

The appropriate coefficients can be calculated as follows:
it can. In this calculation scheme, α _jx, Α_mx, And α
_axRepresents the refractive index of the gas j, and the wavelength λ_xAnd α
_cxThe purge gas or air at
Represents the refractive index of air contaminated by gas. α_cx= (1-c) α_ax+ Cα_mx (13)

The turbulence and contamination of air in the path of the displacement measuring interferometer leads to a change in the observed refractive index of the air in the measuring path. The error E of the measured distance is given by E = (Δα _c1 −KΔ (α _c3 −α _c2 )) L (14)

Here, L is a measurement path of the displacement measurement interferometer.
Is the length of Δα_c1Is the wavelength λ₁Change in refractive index at
And Δ (α_c3−α_c2) Is the wave of the second harmonic interference system
Long λ _TwoAnd λ_ThreeIs the change in the difference in refractive index. Refraction is pressure
Is proportional to the quotient of (p) divided by the absolute temperature (T),
If only the effects of pressure and temperature are considered, then Δα_c1and
Δ (α_c3−α_c2)

(37)

(38) Where ρ = p / T, and Δp is ρ
Is the amount of change.

In view of the change in the relative amount of contamination due to the purge gas, Δc, Δα _c1 and Δ (α _c3 −α _c2 ) are calculated as follows: Δα _c1 = Δc (α _m1 −α _a1 ) (17) Δ (α _{c3 -α c2) = Δc (α} m3 -α a3 -α m2 + α a2) is given by (18).

If σ _ρ is the standard deviation of ρ, the standard deviation (σ _{E, ρ} ) of the error due to turbulence is

[Equation 39] Given by

If σ _c is the standard deviation of c, the standard deviation (σ _{E, c} ) of the error due to the purge gas contamination is σ _{E, c} = σc ((α _m1 −α _a1 ) −K (α _m3 − α _m2 −α _a3 + α _a2 )) given by L (20). The total variance of the length measurements is

(Equation 40) Given by

The optimal value of K is Can be found by setting The resulting optimal value for K is

[Equation 41] Given by

Thus, the value of K given by this formula provides, but is not necessarily, a complete correction for pressure, temperature, and purge gas errors. When the variation in contamination is zero, the above formula changes to formula (5), a formula normally used to correct only pressure and temperature.

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

It should be noted that in this embodiment of the invention, the use of helium or neon alone, or nearly alone, can be used. Thus, the purge gas may include at least 90%, preferably at least 95% or 98%, of helium or neon alone, or a mixture of these gases. Both gases have very low refractive indices and the change in refractive index between wavelengths commonly employed in interferometer devices in lithographic equipment. Contamination of the interferometer measurement area by one of these two gases effectively acts as if the pressure in the chamber is reduced, which is compensated in the usual way by a second harmonic interference device. can do. An advantage of this aspect of the embodiment is that helium and neon, especially helium, are relatively inexpensive gases. further,
When an appropriate coefficient K is calculated, the use of such a coefficient results in little total error.

However, the combination of helium or neon with nitrogen provides an improved system that maintains a low total error, but the errors generated by the two different interferometers cancel each other out much less. Become. This has the added advantage that a smaller error in either of the two interferometers results in a smaller total error in the result generated by the interferometer system. Therefore, alternative purge gases used in this embodiment of the invention include helium and / or a mixture of neon and nitrogen. For example, 90-99% by volume of nitrogen and 1-
A mixture with 10% by volume of helium and / or neon, more preferably 94-96% by volume of nitrogen and 4-6%
It is a mixture with helium and / or neon by volume.

Although particular embodiments of the present invention have been described above, it should be understood that the invention can be practiced otherwise than as described. The above description does not limit the invention.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a lithographic projection apparatus according to an embodiment of the present invention.

FIG. 2 shows a mask stage of the lithographic projection apparatus of FIG. 1 in more detail;

FIG. 3 shows a substrate stage of the lithographic projection apparatus of FIG. 1 in more detail;

[Explanation of symbols]

 CO illuminator optical system LA, Ex, IL radiation system M mask MT mask table PB projection beam PL projection lens system 2-6 space 11 gas supply source 12 reservoir 13 thin film 14, 15, 16 sheet 17 flushing gas supply outlet 18 Exhaust inlet 112-117 Flow controller 122-126 Vacuum pump 127 Vacuum pump

Continued on the front page (72) Inventor Philip Dennis Henshaw United States Massachusetts, Carlisle, East Riding Driving 25 (72) Inventor Engelbertus Antonius Franciscus Van de Pasch Netherlands Oil Shot, van Heersterbeekstraat 8 ( 72) Inventor Marcel Hendricks Maria Boehmes Feldhofen, Lanzer Luberg 37 F-term (reference) 2F065 AA01 CC17 DD04 FF51 PP12 5F046 AA22 BA04 BA05 CB17 CC01 CC02 CC16 DA06 DA07 DA27 DB03 DB05

Claims (30)

[Claims] A radiation system for providing a projection beam of radiation; a patterning means for patterning the projection beam according to a desired pattern; a substrate table for holding a substrate; and a substrate table for holding the patterned beam. A projection system for imaging onto a target portion of the lithographic projection apparatus, the interference operating at a wavelength λ ₁ for measuring the position of the substrate table or of a table that is part of the patterning means. A displacement measuring means, and a flushing gas means for supplying a purge gas to the space to expel the atmosphere from the space,
Means for accommodating at least a part of the substrate table and / or at least a part of the table being part of the patterning means, wherein the purge gas substantially comprises a projection beam of the radiation. And having substantially the same refractive index as air at wavelength λ ₁ when measured at the same wavelength, temperature, and pressure. 2. The method of claim 2, wherein the purge gas is N ₂ , He, A
The device according to claim 1, comprising two or more components selected from r, Kr, Ne, and Xe. 3. The apparatus of claim ₂ , wherein said purge gas comprises at least 95% by volume of N ₂ and at least 1% by volume of He. 4. The apparatus of claim 2, wherein said purge gas comprises at least 95% by volume Ar and at least 1% by volume Xe. 5. The apparatus of claim 2, wherein said purge gas comprises at least 90% by volume Ar and at least 5% by volume Kr. 6. The apparatus of claim ₂ , wherein said purge gas comprises at least 95% by volume N ₂ and at least 1% by volume Ne. 7. The apparatus of claim ₂ , wherein said purge gas comprises at least 50% by volume of N ₂ and at least 35% by volume of Ar. 8. The apparatus of claim ₂ , wherein said purge gas comprises at least 94% by volume of N ₂ , at least 0.5% by volume of He, and at least 0.5% by volume of Xe. 9. A second harmonic interferometer operating at wavelengths λ ₂ and λ ₃ for adjusting the measurements of said interference displacement measuring means to substantially eliminate the effects of pressure and temperature changes. Means, wherein said purge gas comprises three or more different components, each component having the formula: (Equation 2) Where F _j is the refractive index at wavelengths λ ₂ and λ ₃ , wherein F _j is the volume of component j in the purge gas containing a total of k components. Percentage,
α _j1 is the refractive index of component j at wavelength λ ₁ , α _j2 is the refractive index of component j at wavelength λ ₂ , α _j3 is the refractive index of component j at wavelength λ ₃ , α _a1 Is the refractive index of air at wavelength λ ₁ , α _a2 is the refractive index of air at wavelength λ ₂ , α _a3 is the refractive index of air at wavelength λ ₃ , The apparatus according to claim 1, wherein: 10. The method of claim 1, wherein the purge gas is N ₂ , He, A
The apparatus according to claim 9, comprising three or more different components selected from r, Kr, Ne, and Xe. 11. The method of claim 11, wherein the purge gas comprises: (i) 50 to 9;
N ₂ and / or Ar in an amount of 0% by volume; (ii)
Xe and / or Kr in an amount of 0.5-40% by volume;
(Iii) He and / or N in an amount of 2 to 20% by volume
The apparatus of claim 10, comprising e. 12. A radiation system for providing a projection beam of radiation, patterning means for patterning the projection beam according to a desired pattern, a substrate table for holding a substrate, and a substrate table for holding the patterned beam. A projection system for imaging onto a target portion of the lithographic projection apparatus, the interference operating at a wavelength λ ₁ for measuring the position of the substrate table or of a table that is part of the patterning means. A displacement measuring means, and a wavelength λ ₂ for adjusting a measured value of the interference displacement measuring means so as to substantially eliminate the influence of changes in pressure and temperature.
And a second harmonic interferometric means operating at λ ₃ and flushing gas means for supplying a purge gas to the space to expel air from the space,
Means for accommodating at least a part of the substrate table and / or at least a part of the table being part of the patterning means, wherein the purge gas substantially comprises a projection beam of the radiation. , And contains two or more components, each component being represented by the equation Λ ₁ , λ ₂ , and λ ₃ such that α _m1 is the refractive index of the purge gas at wavelength λ ₁ , α _m2 Is the refractive index of the purge gas at wavelength λ ₂ , α _m3 is the refractive index of the purge gas at wavelength λ ₃ , Wherein α _a1 is the refractive index of air at wavelength λ ₁ and α _a2 and α _a3 are as defined in claim 9. 13. The method of claim 12, wherein the purge gas is N ₂ , He, A
The apparatus according to claim 12, comprising two or more gases selected from r, Kr, Ne, and Xe. 14. The method of claim 14, wherein the purge gas comprises: (i) 65-9.
9.5% by volume of the amount of N _2, He, and Ar, and / or Ne, apparatus according to claim 13 including the (ii) 0.5 to 35 volume% of the amount Kr and / or Xe. 15. A radiation system for providing a projection beam of radiation; patterning means for patterning the projection beam according to a desired pattern; a substrate table for holding a substrate; and a substrate table for holding the patterned beam. A projection system for imaging on a target portion of the lithographic projection apparatus, comprising: a flushing gas means for supplying a purge gas to the space to expel the atmosphere from the space;
Means for accommodating at least a part of the substrate table and / or at least a part of the table which is part of the patterning means, wherein the purge gas does not substantially absorb the projection beam of radiation; A wavelength λ for measuring the position of the substrate table or the position of the table which is part of the patterning means.
An interference displacement measuring means operating at ₁ and operating at wavelengths λ ₂ and λ ₃ for adjusting the measured value (DI) of said interference displacement measuring means according to the equation L = (DI) −K (SHI) (9) In the above equation, L is a measured value of the adjusted interference displacement measuring means, SHI is a measured value of the second harmonic interference measuring means, and K Is a coefficient, the value of which is optimized such that the effects of changes in pressure, temperature, and purge gas composition are partially eliminated from the adjusted measurement L. 16. The apparatus of claim 15, wherein said purge gas has a refractive index substantially equal to that of air at wavelength λ ₁ when measured at the same wavelength, temperature, and pressure. 17. K is the equationGiven by where α_mxAnd α_axRespectively
Purge gas or air wavelength λ_xRepresents the refractive index at
α_cxOf the air contaminated by the purge gas by the relative amount c
Wavelength λ_xWhere ρ is the pressure divided by the absolute temperature.
Quotient _ρIs the standard deviation of ρ and σ_cIs c
Apparatus according to claim 15 or 16, which is the standard deviation. 18. Apparatus according to any one of claims 15 to 17, wherein the purge gas comprises at least 95% by volume of He. 19. The apparatus according to claim 15, wherein the purge gas comprises 94 to 96% by volume of N ₂ and 4 to 6% by volume of He. 20.₁Is about 633 nm, and λ_TwoIs about 5
32 nm and λ _ThreeIs about 266 nm.
An apparatus according to any one of the preceding claims. 21. A flushing gas means, comprising: a source of a purge gas as defined in any of the preceding claims; and a gas flow regulator for controlling a flow rate of the purge gas into the space. Apparatus according to any of the preceding claims, comprising: and exhaust means for removing purge gas from the space. 22. The apparatus of claim 21, wherein said flow regulator comprises a flow restrictor. 23. Apparatus according to claim 21 or claim 22, wherein the flow conditioner comprises a blower. 24. The radiation of the projection beam has a radiation intensity of about 18
Less than 0 nm, preferably about 157 nm or 126 nm
Apparatus according to any one of the preceding claims, having a wavelength of 25. providing a substrate at least partially covered by a layer of radiation-sensitive material; providing a projection beam of radiation using a radiation system; and projecting a beam using patterning means. Providing a pattern in its cross-section to the device, and projecting the patterned beam of radiation onto a target area of a layer of radiation-sensitive material, comprising: an interference displacement measuring means operating at a wavelength λ _1. Determining the position of the table using: the table is suitable for holding the substrate or forming part of the patterning means; and housing at least a part of the table Providing a purge gas to the space and expelling the atmosphere therefrom; A method characterized by having a projection beam without substantially absorbing the same wavelength, temperature, and refractive index substantially the same as the refractive index of air at a wavelength lambda ₁ when measured at a pressure of the radiation . 26. The method of claim 25, further comprising using second harmonic interference measuring means operating at wavelengths λ ₂ and λ ₃ to substantially eliminate the effects of pressure and temperature changes. And wherein the purge gas comprises three or more different components, each component having the equation (Equation 8) Where F _j is the refractive index at wavelengths λ ₂ and λ ₃ , wherein F _j is the volume of component j in the purge gas containing a total of k components. Percentage,
α _j1 is the refractive index of component j at wavelength λ ₁ , α _j2 is the refractive index of component j at wavelength λ ₂ , α _j3 is the refractive index of component j at wavelength λ ₃ , α _a1 Is the refractive index of air at wavelength λ ₁ , α _a2 is the refractive index of air at wavelength λ ₂ , α _a3 is the refractive index of air at wavelength λ ₃ , 26. The method of claim 25, wherein 27. Providing a substrate at least partially covered by a layer of radiation-sensitive material, providing a projection beam of radiation using a radiation system, and projecting a beam using patterning means. Providing a pattern in its cross-section, and projecting the patterned beam of radiation onto a target area of a layer of radiation-sensitive material, the interference displacement measuring means operating at wavelength λ _1. Determining the position of a table using the method, wherein the table is suitable for holding the substrate or forming part of the patterning means, and operating at wavelengths λ ₂ and λ ₃ Using the second harmonic interference measuring means, the measurement of the interference displacement measuring means is performed so as to substantially eliminate the influence of pressure and temperature changes. Adjusting a constant value, and purging the space accommodating at least a part of the table.
Providing a gas and expelling air therefrom, wherein the purge gas does not substantially absorb the projected beam of radiation and comprises two or more components, each component having the equation Equation 10 _Where α _m1 is the refractive index of the purge gas at wavelength λ ₁ , and α _m2 has a refractive index at wavelengths λ ₁ , λ ₂ , and λ ₃ that substantially satisfies Is the refractive index of the purge gas at wavelength λ ₂ , α _m3 is the refractive index of the purge gas at wavelength λ ₃ , Where α _a1 is the refractive index of air at wavelength λ ₁ , α _a2 is the refractive index of air at wavelength λ ₂ , and α _a3 is the refractive index of air at wavelength λ _3. The method characterized by the above. 28. Providing a substrate at least partially covered by a layer of radiation-sensitive material; providing a projection beam of radiation using a radiation system; and projecting a projection beam using patterning means. Providing a pattern in its cross-section to the target, and projecting the patterned beam of radiation onto a target area of a layer of radiation-sensitive material, wherein the space comprises at least a portion of a table. Providing a purge gas to expel air therefrom, wherein the table is suitable for holding the substrate or forming part of the patterning means;
The purge gas, and determining a step that does not substantially absorb a projection beam of radiation, the position of said table using interferometric displacement measuring means operating at a wavelength lambda _1, the equation L = (DI) −K (SHI) (9) using the second harmonic interference measuring means operating at wavelengths λ ₂ and λ ₃ , using the measured values (D
Adjusting I), wherein in said equation:
L is the measured value of the interference displacement measuring means after the adjustment, and SHI
Is the value measured by the second harmonic interference measuring means, K is a coefficient, the value of which is partially eliminated from the adjusted value L by the effects of changes in pressure, temperature, and purge gas composition. Optimized in such a way that: 29. A device manufactured according to the method of any one of claims 25 to 28. 30. Claims 3 to 8, claim 11,
A purge gas as defined in any one of claims 14, 18, or 19.