KR20020006591A - Lithographic apparatus, device manufacturing method, device manufactured thereby and gas composition - Google Patents

Abstract

PURPOSE: A lithographic projector is provided to accurately obtain a position of a movable table in the projector, by using two or more color interferometer devices by an arbitrary selection. CONSTITUTION: The apparatus comprises flushing gas means for supplying purge gas to a space accommodating at least a part of the movable table, the purge gas being selected such that leakage of the purge gas into the area of operation of the interferometric devices does not cause significant error in the interferometric measurements.

Description

Lithographic projection apparatus, device manufacturing method, device and gas composition produced by this {LITHOGRAPHIC APPARATUS, DEVICE MANUFACTURING METHOD, DEVICE MANUFACTURED THEREBY AND GAS COMPOSITION}

The present invention

A radiation system for supplying a projection beam of radiation;

Patterning means for patterning the projection beam according to a predetermined pattern;

A substrate table for holding the substrate; And

A lithographic projection apparatus comprising a projection system for imaging a patterned beam on a target area of a substrate.

The term "patterning means" is used broadly as meaning means that can be used to impart an incident radiation beam with a patterned cross section corresponding to a pattern to be produced in a target area of the substrate; It may also be used herein as the term "light valve". In general, the pattern will correspond to a specific functional layer in a device formed in the target area, such as an integrated circuit or other device (see below). Examples of such patterning means include the following.

-Mask table for fixing the mask. The concept of masks is already well known in the lithography field and includes binary, alternating phase-shift and attenuated phase-shift masks and various hybrid mask types. When such a mask is placed in the radiation beam region, selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of radiation incident on the mask is achieved according to the pattern of the mask. The mask table may be fixed at a predetermined position in the area of the incident beam of radiation and will allow it to move relative to the beam if necessary.

Programmable mirror arrangement. An example of such a device is a matrix-addressable surface with a viscoelastic control layer and a reflective surface. The basic principle of such a device is that incident light is reflected as diffracted light in the (eg) addressed region of the reflecting surface while incident light is reflected as undiffracted light in the unaddressed region. Using an appropriate filter, the non-diffracted light can be filtered out of the beam where the non-diffracted light is reflected. 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 any suitable electronic means. More information regarding such mirror arrangements can be obtained, for example, from US Pat. Nos. 5,296,891 and 5,523,193, which are incorporated herein by reference.

Programmable LCD Array. An example of such a structure is in US Pat. No. 5,229,872, which is incorporated herein by reference.

For the purpose of simplicity of explanation, any of the remainder of this specification may, by itself, be referred to as exemplary terms including masks and mask tables. However, the general principles discussed in such examples should be understood in the broad sense of the patterning means as described above.

Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In this case, the patterning means can produce a circuit pattern corresponding to an individual layer of the integrated circuit, which pattern is comprised of one or more dies on a substrate (silicon wafer) coated with a layer of radiation sensing material (resist). It may be missing in the area. In general, an entire network of adjacent target areas is formed on one wafer, and these target areas are continuously irradiated one at a time through a mask. Current devices employing patterning by masks on a mask table can be divided into two types of devices. In one type of lithographic projection apparatus, each target region is irradiated by exposing the entire mask pattern onto the target region at one time. Such an apparatus is commonly referred to as a wafer stepper. An alternative device, commonly referred to as a step-and-scanapparatus, progressively scans the reticle pattern under a projection beam in a predetermined reference direction ("scanning" direction), while in the same direction as the scanning direction or Each target area is irradiated by synchronously scanning the substrate table in the opposite direction. Since the projection system generally has a magnification factor M (generally < 1), the speed V at which the substrate table is scanned is a factor M times that at which the mask table is scanned. More detailed information relating to the lithographic apparatus described herein can be found in US Pat. No. 6,046,792, which is incorporated herein by reference.

In a manufacturing process using a lithographic projection apparatus, a pattern (eg, a mask pattern) is imaged on a substrate on which a layer of radiation sensing material (resist) is applied even at a minimum. Prior to this imaging step, the substrate may be subjected to various procedures such as priming, resist application and soft bake. After exposure, there will be other procedures such as post-exposure bake (PEB), development, hard bake and measurement / inspection of the imaged shape. This series of procedures is used, for example, as the basis for patterning individual layers of IC devices. The patterned layer is then subjected to all the various processes for finishing individual layers such as etching, ion implantation (doping), metallization, oxidation, chemical-mechanical polishing, and the like. If several layers are required, the whole process or its modification process will have to be repeated for each new layer. In the end, an array of devices will be present on the substrate (wafer). After these devices are separated from each other by a technique such as dicing or sawing, each device may be mounted on a transport apparatus and connected to a pin. Further information on such a process can be obtained, for example, from "Microchip Fabrication: A Practical Guide to Semiconductor Processing (3rd edition, Peter van Zant, McGraw Hill Publishers, 1997, ISBN 0-07-067250-4)" It is also adopted in the present specification.

For simplicity of explanation, the projection system will hereinafter be referred to as the "lens". However, the term should be interpreted broadly as encompassing various types of projection systems, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components that operate in accordance with any of the principles of directing, shaping or controlling the projection beam of radiation, and in the following description collectively or separately for these components are referred to as "lenses." Will be mentioned. The lithographic apparatus may also be of a type having two or more substrate tables (and / or two or more mask tables). In such "multi-stage" devices, one or more additional tables will be used in parallel or preliminary steps while one or more other tables are being used for exposure. For example, US 5,969,441 and WO 98/40791 disclose twin stage lithographic apparatus and are employed herein.

In order to reduce the size of the shape that can be imaged, it is desirable to reduce the wavelength of illumination radiation. Thus, wavelengths smaller than 180 nm are used, for example wavelengths of 157 nm or 126 nm. However, this wavelength is strongly absorbed by the normal atmosphere, which causes an unacceptable loss of intensity as the beam crosses the device. In order to solve this problem, it has previously been proposed to flush the device with a stream of gas which is actually transparent to the wavelength of transmission, for example nitrogen (N ₂ ).

The lithographic projection apparatus may comprise interferometric displacement measuring means used to accurately measure the position of the movable table, such as a mask or substrate table. These means measure the optical path length (geometric distance x refractive index) in a movable table using a measuring beam of coherent monochromatic radiation. The measuring means are very sensitive to pressure and temperature and changes in the composition of the medium through which the measuring beam passes. All three changes affect the refractive index of the medium. Typically, a second harmonic interferometric device is used to account for the change in refractive index caused by temperature and pressure variations. More detailed information about such a second harmonic interferometer 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.

Alternatively, a second harmonic interferometer can compensate for the change in composition of the medium. However, the second interferometer device cannot simultaneously account for pressure and temperature changes and composition changes in the medium.

Certain spaces in the projection device may be cleaned using purge gas to remove certain gases, such as oxygen or water, that absorb radiation at the wavelength of the radiation projection beam. The inventors found that if the gas used to purify the system enters the region in which the interferometer displacement measuring means operates, the refractive index of these regions changes and the position measurement is affected. In order to keep the measuring means operating at the required high accuracy, any change from the refractive index of the medium can be avoided.

It is an object of the present invention to provide a lithographic projection apparatus in which the discharge of purge gas does not affect the interferometer displacement measuring means.

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

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

3 illustrates the substrate stage of the lithographic projection apparatus of FIG. 1 in more detail.

This and other purposes

Interferometer displacement measuring means operating at a wavelength λ ₁ for measuring the position of the substrate table or the position of the table that is part of the patterning means;

-Further comprising flushing gas means for supplying a purge gas to displace ambient air therefrom in at least a portion of the substrate table and / or in a predetermined space containing at least a portion of the table, wherein the purge gas The present invention in a lithographic apparatus as stated in the opening paragraph, characterized in that it is substantially absorptive to said radiation projection beam and has a refractive index at a wavelength λ ₁ equal to the refractive index of air measured at substantially the same wavelength, temperature and pressure. Is achieved according to.

For example, the inventors have measured the interferometer displacement measurement means by 180 nm or less by flushing a mask and substrate stage, typically comprising a movable mask and a substrate table, respectively, with a particular gas composition having a refractive index equal to the refractive index of air under the same measurement conditions. It has been found that it can operate at a certain accuracy while the use of radiation having a wavelength of is allowed.

According to another embodiment of the present invention, a second harmonic interferometer operating at wavelengths λ ₂ and λ ₃ for adjusting the measurement of the interferometer displacement measuring means which substantially eliminates the effects of pressure and temperature changes as described above. An apparatus is further provided which further comprises measuring means, wherein the purge gas comprises at least three different components each having a refractive index at wavelengths λ ₂ and λ ₃ where the following equations are fully satisfied.

Where F _j is the portion of the total of component j in the purification gas, the purification gas contains the total of the k components, α _j1 is the refractive index of component j at wavelength λ ₁ , and α _j2 is the wavelength (λ ₂ ) is the refractive index of component j at), 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 , and α _a2 is the wavelength (λ The refractive index of air at ₂ ) and α _a3 is the refractive index of air at wavelength λ ₃ ; And where:

to be.

Where there is a second harmonic interferometer in the device, simply adjusting the refractive index of the purification gas to the refractive index of air at the displacement measurement interferometer operating wavelength is not sufficient to overcome the displacement measurement error caused by leakage of the purification gas. . The inventors therefore devised a purge gas composition in which each component typically comprises at least three different elements having sufficiently different refractive properties, where the refractive index is defined as refractive index-1. Proper selection of the gas that satisfies the above equation or generally satisfies, the change in the constituents of the purification gas will not affect or generally affect the measurement of any interferometer. Thus, accurate position measurements can be obtained taking into account changes in temperature, pressure and leakage of the purge gas.

According to another form of the invention

Interferometer displacement measuring means operating at a wavelength λ ₁ for measuring the position of the substrate table or the position of the table which is part of the patterning means;

Second harmonic interferometer measuring means operating at wavelengths λ ₁ and λ ₂ which adjust the measurement of the interferometer displacement measuring means to substantially eliminate the effects of pressure and temperature changes;

-Flushing gas means for supplying a purge gas to displace ambient air therefrom in at least a portion of the substrate table and / or in a predetermined space containing at least part of the table, wherein the purge gas Contain at least two components which are nonabsorbable to the projection beam and each having refractive indices at wavelengths λ ₁ , λ ₂ and λ ₃ which are generally satisfied

Where α _ml is the refractive index of the purification gas at the wavelength λ ₁ , α _m2 is the refractive index of the purification gas at the wavelength λ ₂ , and α _m3 is the refractive index of the purification gas at the wavelength λ ₃ ,

Wherein α _al 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 lithographic projection apparatus as described at the outset is provided.

In this form, no measurement interferometer or second harmonic interferometer is required to provide accurate measurement displacements that account for contamination of the purification gas. Rather, this form ensures that the entire interferometer system is adjusted to account for the effects of purge gas contamination. This is obtained by off-setting the error in the displacement measuring interferometer with the error of the second harmonic interferometer. This form of the present invention provides an alternative way in which the effects of temperature, pressure and leakage of the purge gas can be accurately calculated after the measurement of the interferometer and provides for a simpler gas mixture to be used, for example just a mixture of two different gases. Allow.

According to a further aspect of the invention

Supplying a substantially non-absorbing purge gas to the radiation projection beam to displace ambient air therefrom in a predetermined space containing at least a portion of the substrate table and / or a portion of the table that is at least part of the patterning means. Flushing gas means for;

Interferometer displacement measuring means operating at a wavelength λ ₁ for measuring the position of the substrate table or the position of the table that is part of the patterning means; And

Second harmonic interferometer measuring means operating at wavelengths λ ₂ and λ ₃ for adjusting the measurement of the displacement measuring means DI according to the following equation,

L = (DI)-K (SHI)

Where L is the measured interferometer displacement measuring means, SHI is the measurement of the second harmonic interferometer measuring means, and K is the effect of the change in the adjusted pressure, temperature and purification gas composition whose value is removed from the measurement (L). Coefficients that are optimized.

In this aspect of the invention, the coefficient K is optimized to give a minimum error to the length measurement L. This embodiment is less stringent than the first three embodiments of the present invention in that it is a specific combination of gases to be used, and thus provides a more cost effective way in which errors due to constitutive changes in the purification gas can be reduced.

According to another form of the invention

Providing a substrate at least partially applied by a layer of radiation sensing material;

Providing a projection beam of radiation using a radiation system;

Using patterning means for imparting a cross-sectional pattern to the projection beam;

Projecting a patterned beam of radiation onto a target area of the layer of radiation sensing material,

Determining the position of a table suitable for supporting the substrate or forming part of the patterning means using interferometric displacement measuring means operating at wavelength λ ₁ ;

A wavelength lambda substantially equal to the refractive index of the air measured at the same wavelength, temperature and pressure, which is substantially absorptive to the radiation projection beam in order to displace the ambient air therefrom in a space containing at least a portion of the table; A device manufacturing method is provided, further comprising providing a purge gas having a refractive index in ₁ ).

In a preferred embodiment, the method comprises adjusting the measurement of the interferometer displacement measuring means to substantially eliminate the effects of pressure and temperature changes using second harmonic interferometer measuring means operating at wavelengths λ ₂ and λ ₃ . It further includes. In the present embodiment, the purification gas includes three or more components each having refractive properties at wavelengths λ ₂ and λ _{3 in} which the equation below is substantially satisfied.

(Equation 1)

(Equation 2)

Where F _j is the portion of the total of component j in the purification gas, the purification gas comprises the total of the k components, α _j1 is the refractive index of component j at wavelength (λ ₁ ), and α _j2 is the wavelength (λ ₂ ) is the refractive index of component j at), 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 , and α _a2 is the wavelength λ The refractive index of air at ₂ ) and α _a3 is the refractive index of air at wavelength λ ₃ ; And where:

(Equation 3)

to be.

Another form of the invention

Providing a substrate at least partially applied by a layer of radiation sensing material;

Providing a projection beam of radiation using a radiation system;

Using patterning means for imparting a cross-sectional pattern to the projection beam;

Projecting a patterned beam of radiation onto a target area of the layer of radiation sensing material,

Determining the position of a table suitable for supporting the substrate or forming part of the patterning means using interferometric displacement measuring means operating at wavelength λ ₁ ;

Adjusting the measurement of said interferometer displacement measuring means to substantially eliminate the effects of temperature and pressure changes using second harmonic interferometer measuring means operating at wavelengths λ ₂ and λ ₃ ;

At a wavelength λ ₁ , λ ₂ and λ ₃ substantially non-absorbing with respect to the radiation projection beam and substantially satisfying the following equation for displacing the ambient air therefrom in at least a space for receiving a portion of the table: Supplying a purge gas comprising two or more components each having refractive properties,

(Equation 4)

Where α _ml is the refractive index of the purification gas at the wavelength λ ₁ , α _m2 is the refractive index of the purification gas at the wavelength λ ₂ , and α _m3 is the refractive index of the purification gas at the wavelength λ ₃ ,

(Equation 5)

Wherein α _al 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 device manufacturing method is provided.

Another form of the invention

Providing a substrate at least partially applied by a layer of radiation sensing material;

Providing a projection beam of radiation using a radiation system;

Using patterning means for imparting a cross-sectional pattern to the projection beam;

Projecting a patterned beam of radiation onto a target area of the layer of radiation sensing material,

Supply a purge gas that is substantially nonabsorbing with respect to the projection beam of radiation to displace ambient air therefrom in a space suitable for supporting the substrate or containing at least a portion of a table forming part of the patterning means; Making;

Determining the position of the table using interferometric displacement measuring means operating at wavelength λ ₁ ; And

Adjusting the measurement of said interferometer displacement measuring means using a second harmonic interferometer measuring means operating at wavelengths λ ₂ and λ ₃ according to the following equation,

(Equation 9)

L = (DI)-K (SHI)

Where L is the measured interferometer displacement measuring means, SHI is the measurement of the second harmonic interferometer measuring means and K is the coefficient so that the effect of pressure, temperature and purge gas composition changes is removed from the adjusted value (L). Is optimized.

While the use of the device according to the invention may be made in the manufacture of ICs herein, it should be clearly understood that such devices may have many other possible applications. For example, the device may include sensing patterns for integrated optical systems, guidance and magnetic domain memory, liquid-crystal display panels, thin-film magnetic heads, and the like. It can be used in the manufacturing process of. One skilled in the art, within the context of this alternative application, uses some of the terms "reticle", "wafer" or "die" herein to the more general terms "mask", "substrate" and "target area", respectively. It should be understood as a substitute. As used herein, the terms transmitted radiation and transmitted beam include not only particle beams such as ion beams or electron beams, but also ultraviolet radiation (eg, ultraviolet radiation having a wavelength of 365, 248, 193, 157 or 126 nm) and EUV. Includes all types of electromagnetic radiation.

First embodiment

1 schematically depicts a lithographic projection apparatus according to a particular embodiment of the invention. The device is:

A radiation system (LA, Ex, IL) for supplying a projection beam of radiation (e.g. U.V. or E.U.V. radiation, radiation having a wavelength less than 180 nm, for example approximately 157 nm or 126 nm);

A first object table (mask table) MT mounted with a mask holder for fixing a mask MA (e.g. a reticle) and connected to first positioning means for accurately positioning the mask with respect to the item PL. ;

A second object table (substrate) mounted with a substrate holder for holding the substrate W (e.g. a resist coated silicon wafer) and connected to second positioning means for accurately positioning the substrate with respect to the item PL. Table) (WT);

A projection system ("lens") PL (for example of a mirror group) for drawing the irradiated portion of the mask MA on the target area C (including one or more dies) of the substrate W Reflective or catadioptric system).

As mentioned above, the device is transmissive (ie with a transmissive mask). In general, however, the apparatus may be reflective, for example, with a reflective mask. Alternatively, the apparatus may use another kind of patterning means, such as a programmable mirror arrangement of the type described above.

The radiation system comprises a radiation source LA (eg a mercury ramp or excimer laser) that produces a radiation beam. The beam is fed to the lightcasting system (lightcaster) IL either directly or after passing through a conditioning means such as, for example, a beam expander Ex. The transmitter IL comprises adjusting means AM for setting the outer and / or inner radial magnitude (commonly referred to as sigma-outer and sigma-inner, respectively) of the beam intensity distribution. It also generally contains various components such as an integrator IN and a collector CO. In this way, the beam PB incident on the mask MA has a uniformity and intensity distribution in its cross section.

1, the radiation source LA is placed in the housing of the lithographic projector (e.g. sometimes as if the radiation source LA is a mercury lamp), but it is far from the lithographic projection apparatus and the radiation it produces The beam may be brought into the device (eg by means of a suitable directional mirror). The present invention and claims encompass both of these cases.

The beam PB blocks the mask MA fixed to the mask holder on the mask table MT. The beam PB across the mask MA passes through the lens PL that focuses the beam PB on the target region C of the substrate W. By means of the second positioning means (and interferometer measuring means IF comprising an interferometer displacement measuring device operating at a wavelength λ ₁ , for example about 633 nm), the substrate table WT is, for example, a beam ( It can be accurately moved to position different target areas C in the path of PB). Similarly, the first positioning means is capable of accurately positioning the mask MA with respect to the path of the beam PB, for example, after mechanically withdrawing the mask MA from the mask library or during scanning. Can be used. In general, the movement of the objective tables MT, WT will be done with the help of a long stroke module (coarse positioning) and a short stroke module (fine positioning), although not clearly shown in FIG. . However, in the case of a wafer stepper (as opposed to a step-and-scan apparatus), the mask table MT may be connected or fixed to a single stroke actuator.

The apparatus described above can be used in two different modes:

1. In the step mode, the mask table MT is basically kept stationary, and the entire mask image is projected to the target area C at once (ie, with a single "flash"). Subsequently, the substrate table WT is shifted in the x and / or y directions so that different target regions C may be irradiated by the beam PB.

2. In the scan mode, the same scenario applies, except that the predetermined target area C is not exposed in a single "flash". Instead, the mask table MT is movable in a predetermined direction (so-called " scanning direction &quot;, for example, y direction) at a speed of ν so that the projection beam PB scans all parts of the mask image, At the same time, the substrate table WT simultaneously moves in the same direction or the opposite direction at a speed V = Mv, where M is the magnification of the lens PL (usually M = 1/4 or M = 1/5). In this way, a relatively large target area C can be exposed without degrading the resolution.

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

Masks made of ceramic material such as Zerodur (RTM) and supported in recesses of the mask table MT properly arranged by a drive system (not shown) while the lithographic apparatus is in operation ( M) will be shown. The mask table MT receives the wafer W (shown in FIGS. 1 and 3) from the last element of the collimation optic CO generating the projection beam PB and the projection beam PB passing through the mask M. FIG. Sandwiched between a first element of a projection lens system PL projecting onto it.

The mask stage can be divided into regions or spaces of 2 to 6 as follows: The space 2 is between the final light projector optics CO and the mask table MT; The space 3 is within the mask table MT above the mask M; The space 4 is within the mask table MT between the mask M and the pellicle 13; The space 5 is within the mask table MT under the pellicle 13; And the space 6 is between the mask table MT and the projection lens system PL. Each of these spaces is flushed with a purge gas provided from the gas source 11 by individual flow regulators 112-116. On the other side of each space, the purge gas is transferred to a reservoir 12 by individual vacuum pumps 122-126. The reservoir 12 may be partitioned to allow the use of controlled gases within the selected space, and the device 12a may be included to purify or purge the recycled gas.

If necessary, the various spaces within the mask stage can be separated from each other to ensure laminar flow. For example, a thin sheet of CaF or molten SiO ₂ may be provided to apply the mask table MT and to separate the space 2 in the space 3. Similarly, the sheets 15 and 16 are used to separate the spaces 5 and 6, respectively, and apply the non-planar surface of the first element of the projection lens system PL.

Appropriate conduits are provided in the body of the mask table for supplying and removing gas flows into the internal spaces 3, 4 and 5 of the mask table MT. When the mask table is exposed to air, such as during periods when the device is inoperable or after a mask change, the purge gas is exposed to flush out any air that may have accumulated on, for example, non-flat portions of the mask table. Mechanism is supplied for a short period.

3 shows a wafer stage of the lithographic apparatus of FIG. 1. In order to avoid the problem of providing a purge gas path covering the entire range of movement of the wafer stage, the flushing gas feed outlet 17 and the exhaust inlet 18 are located on the bottom of the projection lens system PL on either side of the final element. Is mounted on. Outlet 17 and inlet 18 are connected to gas source 11 and reservoir 12 by flow regulator 117 and vacuum pump 127, respectively. The inlet 18 and especially the outlet 17 may be provided with vanes for guiding the purge gas flow. If not flat, the final element of the projection lens system PL can be covered with a thin sheet as described above.

The flow regulators 112-117 may include static or controllable pressure or flow reducers and / or blowers required to provide the gas flow rates needed for certain embodiments and available gas supplies.

According to the invention, the mask stage and / or the substrate stage of the apparatus can be washed with a purge gas. Purification gas typically comprises a mixture of two or more gases selected from N ₂ , He, Ne, Ar, Kr and Xe. The gas composition used is substantially transparent to the UV radiation of the projection beam wavelength and is measured under the same conditions of temperature and pressure (e.g. standard clean room conditions) and air when using the same wavelength of radiation. It has a refractive index substantially the same as the refractive index of. The refractive index should be equal to the refractive index of air at the wavelength of the radiation beam used in the interferometer displacement measuring means IF. The pressure of the purge gas in the mask and / or substrate stage may be atmospheric pressure, or it may be such atmospheric pressure such that any leaking air results in outflow of the gas rather than contaminating the system.

In order to determine which mixture of gases is suitable for use in the present invention, the refractive index of the mixture must be known. The refractive index n ₁ of a k gas mixture at a particular partial pressure, temperature and at a specific wavelength λ ₁ can be determined using the following equation:

Here, n _j1 is the refractive index of the pure gas j at the wavelength λ ₁ .

The refractive index α is related to the refractive index n by the following equation.

Thus, for a mixture of k gas

Where Fj is the relative volume concentration of the gas j and α _j1 is the refractive index of the pure gas j of the wavelength λ ₁ . Therefore, if the purifying gas consists of a mixture of x and y gases for the purposes of this embodiment of the present invention, the relative volume concentrations of the two gases will be in accordance with the following equation.

Α _a1 is the refractive index of air at the wavelength λ ₁ . Or more generally,

(Equation 1)

Where F _j , α _j1 and α _a1 are as described above, where

(Equation 3)

to be.

Refractive and refractive indices are dependent on pressure, temperature and wavelength. Thus, all values of n and α used in the above formulas and all other formulas mentioned herein must be related to the same temperature and pressure. The wavelength λ ₁ used in the calculation should be at least equal to the wavelength of one of the radiation beams of the interferometric displacement measuring means.

Suitable gas mixtures according to the above formulas are mixtures comprising N ₂ and He by volume of 5% by volume, preferably from 2% by volume to 3% by volume; 1 vol% to 5 vol%, preferably 3.5 vol% to 2.5 vol% Ne; Or 35 vol% to 50 vol%, preferably 40 vol% to 45 vol% Ar; A mixture comprising Ar and from 1 vol% to 5 vol%, preferably from 2 vol% to 3 vol% Xe; A mixture comprising Ar and 5 vol% to 10 vol%, preferably 6 vol% to 8 vol% Kr; And a mixture comprising N 2, from 0.5 volume% to 3 volume% He and from 0.5 volume% to 3 volume% Xe. To use a wavelength of 633 nm, preferred gas mixtures include those arranged in Table 1 below. All figures are% by volume.

Yes N2 He Ne Ar Kr Xe 1 2 3 4 5 97.397.059.0 2.7 3.0 41.097.592.9 7.1 2.5

Second embodiment

In this embodiment of the same invention as in the first embodiment except as described below, the interferometer measuring means IF comprises an interferometer displacement measuring device and a second harmonic interferometer device. The second harmonic interferometer device measures the refractive index of the atmosphere in the device at two different wavelengths. In this way it is possible to determine the effects of pressure and temperature with respect to refractive index and therefore to properly adjust the measurement of the displacement interferometer to calculate this change.

This multiplies the second harmonic interferometer to measure the coefficient (K _a) is obtained as a ppaejum this value from the displacement interferometer measurement.

(Equation 9)

L = (DI)-K (SHI)

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 as follows:

(Equation 5)

Where a _ay is the refractive index of the air at wavelength λ _y , where the interferometer displacement measuring means is operated at wavelength λ ₁ and the second harmonic interferometer measuring means is operated at wavelengths λ ₂ , λ ₃ Typically the wavelength λ ₂ is greater than the wavelength λ ₃ . For example, λ ₂ is approximately 532 nm and λ ₃ is approximately 266 nm, typically, λ ₁ is different from λ ₂ and λ ₃ . However, it is possible for λ ₁ to be equal to λ ₂ or equal to λ ₃ .

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

Selecting a purge gas having the same refractive index (or refractive index) as air at wavelength λ ₁ ensures that the displacement interferometer device is accurate even when the purge gas leaks into the measurement area. However, leakage of the purification gas still makes the refractive index measurements at wavelengths λ ₂ and λ _{3 in} which the second interferometer operate. In turn, this may cause an error in the final position measurement. This embodiment of the present invention can address this problem by ensuring that leakage of the purge gas does not affect any interferometer device. This can be achieved by using a purge gas that contains three or more k gases and meets or substantially satisfies the following three equations.

(Equation 1)

(Equation 2)

(Equation 3)

Where F, α, j and k are as described above.

By simultaneously solving the above three equations, the required fraction 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 is equal to the refractive index (or refractive index) of air measured at the same wavelength, temperature and pressure.

Mixtures of suitable gases for use in this example include three or more mixtures with different refractive properties. For example, a purge gas may contain one or more elements having a refractive index of less than 1 × 10 ⁻⁴ at wavelengths of 200 nm to 700 nm and two having a refractive index of greater than 1 × 10 ⁻⁴ at wavelengths of 200 nm to 700 nm. It contains the above elements. Typically, elements with refractive index less than 1 × 10 ⁻⁴ at wavelengths from 200 nm to 700 nm will be present in amounts ranging from 1% to 40% (preferably between 2% and 20% of the volume) and up to 200nm to 700nm At least two elements with refractive index greater than 1 × 10 ⁻⁴ at a wavelength of will be present in an amount of 60% to 90% (preferably 80% to 98% of the volume).

For example, the purification gas includes three or more gases selected from N ₂ , He, Ne, Ar, Kr and Xe. Typically, the purification gas may include He and / or Ne with two or more gases selected from N _2, Ar, Kr and Xe. More preferably, the purification gas is He and / or Ne; Ar and / or N ₂ ; And Kr and / or Xe.

Typically, the purge gas is He and / or Ne in an amount of 1% to 40% (preferably 2% to 20%, more preferably 4% to 16%) of the volume and 60% to 99% (of the volume). Preferably from 80% to 98%, more preferably from 84% to 96%) of at least two gases selected from N _2, Ar, Kr and Xe. For example, the purge gas may be in amounts of 2% to 20% of He and / or Ne (preferably 4% to 16%); Ar and / or N _{2 in an} amount of 50% to 96% (preferably 60% to 92%) of the volume; And Kr or Xe in an amount of 2% to 40% (preferably 3% to 30%) of the volume. Most preferably, the purge gas is He and / or Ne in an amount of 2% to 20%, preferably 4% to 16% of the volume; (i) with 50% to 70% by volume of Ar and / or N ₂ and 10% to 40% by volume of Kr; Or (ii) an amount of Ar and / or N _{2 in an} amount of 70% to 90% of the volume and Xe in an amount of 0.5% to 20% of the volume.

Preferred purge gases according to this embodiment include those arranged in Table 2 below. All numbers represent% of volume.

Yes N2 He Ne Ar Kr Xe 678910111213 66.460.787.184.9 12.79.58.83.9 15.912.110.64.7 67.663.191.490.4 20.423.423.024.8 4.24.54.84.9

Third embodiment

In the third embodiment of the present invention, which is identical to the first embodiment except as described below, the second harmonic interferometer device is used to adjust the measurement of the displacement interferometer to account for temperature and pressure changes. The second harmonic interferometer device has been described in the second embodiment. In this third embodiment, the response of the entire interferometer system is adjusted to account for purge gas contamination. The above is accomplished by offsetting the error caused by the purification gas contamination of each of the two interferometer devices.

In this embodiment, at least two elements make up the purge gas and the following equation should be largely satisfied.

(Equation 4)

Wherein α _m1 , α _m2 and α _m3 are as described above; And

(Equation 5)

Here, α _a1 , α _a2 and α _a3 are as described above. Regarding the first embodiment and the second embodiment, the sum of the gas fractions should be equal to one. therefore,

(Equation 3)

Where F, j and k are as described above.

The refractive index of the purification gas for the wavelength λ ₁ is given by

For the wavelength λ ₂ the refractive index is given by

And the refractive index with respect to the wavelength λ ₃ is

The following conditions are given.

(Equation 3)

The composition of the other purification gas can be calculated by combining the formulas (10), (11) and (12) with the expressions (3), (4) and (5) being satisfied. More information related to refractive properties can be found, for example, by Max Born & Emil Wolf, published in Pergamon Press Oxford, incorporated herein by reference, the principles of optics, the electrical theory of radio interferences, and the diffraction of light. See theory of propagation interference and diffraction of light. Suitable gas mixing includes mixing two or more components with different refractive indices. For example, a purge gas may include one or more elements having a refractive index of less than 3 × 10 ⁻⁴ at a wavelength of 200 nm to 700 nm and a component having a refractive index of greater than 3 × 10 ⁻⁴ at a wavelength of 200 nm to 700 nm. It includes more. Typically, at least one component having a refractive index of less than 3 × 10 ⁻⁴ at a wavelength of 200 nm to 700 nm will be present in an amount of 50% to 99% of the volume and greater than 3 × 10 ⁻⁴ at a wavelength of 700 nm at 200 nm. At least one component having from about 1% to about 50% by volume will be present. The refractive index (or refractive index) of the purification gas mixture at wavelength λ ₁ is different from that of air measured at the same wavelength, temperature and pressure. different.

For example, the purification gas includes two or more gases selected from N ₂ , He, Ne, Ar, Kr and Xe. Typically, the purification gas comprises one or more gases selected from N ₂ , He, Ne and Ar with Kr and / or Xe.

Typically, the purge gas is in an amount from 50% to 99% of the volume, preferably from 65% to 98% of N ₂ , He, Ne and / or Ar and from 1% to 50% of the volume, preferably 2 % And 35% Kr and / or Xe. For example, the clarification gas contains N ₂ , He, Ne and / or Ar in an amount of 65% to 90% of the volume and Kr in an amount of 10% to 35% of the volume. Alternatively, the purge gas contains N ₂ , He, Ne and / or Ar corresponding to 90% to 98% of the volume and Xe corresponding to 2% to 10% of the volume.

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

Yes N2 He Ne Ar Kr Xe 1415161718192021 78.695.7 82.196.6 69.893.4 76.495.2 21.417.930.223.6 4.33.46.64.8

Fourth embodiment

According to a further embodiment of the present invention, which is identical to the first embodiment except as described below, an apparatus may be used which typically only partially compensates for the effects of temperature, pressure and purge gas contamination. This embodiment may in particular relate to the portion where the cost or solubility of certain components of the preferred purification gas, for example Kr or Xe, is prohibited.

In this embodiment, the correction for explaining the pressure and temperature changes is not so accurate, but the correction constant K determined by the second harmonic interferometer device can be optimized since the error caused by the purification gas contamination is corrected to a certain limit. . Therefore, simultaneous correction of pressure, temperature and purge gas errors using an approximation of the second harmonic interferometer coefficients is used.

The approximation coefficient can be calculated as described below. In this calculation, α _jx , α _mx and α _ax represent the refractive index of the purification gas or air of gas j at wavelength λ _x , respectively, and α _cx is the air contaminated by the relative amount c of the purification gas. Indicates the refractive index of:

Air turbulence and contamination in the displacement measurement interferometer path results in changes in the observed reflectivity of the air in the particular path. The error (E) in the measured distance is given by

Where L is the length of the measurement path of the displacement measuring interferometer, Δα _c1 is the refractive change in wavelength λ ₁ , and Δ (α _c3 -α _c2 ) is the wavelength λ ₂ and λ ₃ of the second harmonic interferometer system. Is the refractive index difference between The refractive index is proportional to the phase pressure p at the absolute temperature, so only the pressure and temperature effects are explained and Δα _c1 and Δ (α _c3 -α _c2 ) are given by the following equation.

Where ρ = p / T and Δρ is the ρ change.

When explaining the change in the relative amount of contamination by the purification gas, Δc, Δα _c1 and Δ (α _c3 -α _c2 ) are given by the following equations.

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

If σ _c is the standard deviation of c, then the standard deviation of the error due to the purification gas contamination (σ _{E, c} ) is given by the following equation.

The total change in length measurement is given by

The optimal value of K is You can find out by setting The resulting optimal value for K is given by

Thus, the value of K obtained by the above equation is not necessarily complete but provides simultaneous correction of pressure, temperature and purge gas errors. When the change in contamination is zero, the equation removes equation (5) used to calibrate only pressure and temperature.

The purification gas used in the present embodiment may have a refractive index different from that of air at the wavelength λ ₁ . In another form of this embodiment, the purge gas has a refractive index at a wavelength λ _{1 that} is similar to or substantially the same as the refractive index of air at the same wavelength, temperature, and pressure.

It should be understood that either helium or neon alone or one dominant use may be used in this embodiment of the present invention. The purge gas may thus comprise at least 90%, preferably at least 95% or 98% of helium or neon or a mixture of these gases. All of the gases have very low refractive index, and generally there is little change in the refractive index of the gas between wavelengths used in the interferometer device in the lithographic apparatus. Contamination of the interferometric measuring zone with one of these two gases acts as effectively as the pressure in the chamber is relieved, which can be compensated in a conventional manner by the second harmonic interferometer device. An advantage of the form of this embodiment is that helium and neon, in particular helium, are relatively cheap gas. Also, when the approximation coefficient K is calculated, the use of such coefficients results in very little total error.

However, the combination of nitrogen-containing helium or neon provides an improved system with a low overall error, but the errors caused by two different interferometers are very small in amount offset against each other. This has the additional advantage that the small partial error of either of the two interferometers can result in a smaller overall error as a result of the interferometer system. Thus, alternative purge gases used in embodiments of the present invention comprise a mixture of nitrogen and helium and / or neon. For example, a mixture of 90% to 99% nitrogen by volume and 1% to 10% helium and / or neon by volume, or more preferably 94% to 96% nitrogen by volume and 4% to 6% by volume. A mixture of helium and neon.

While specific embodiments of the invention have been described above, it should be understood that the invention may be practiced otherwise than as described. The description is not intended to be limited to the above invention.

According to the present invention, the discharge of the purge gas does not affect the interferometer displacement measuring means.

Interferometer displacement measuring means operating at a wavelength λ ₁ for measuring the position of the substrate table or the position of the table that is part of the patterning means,

To replace the atmosphere, flushing gas means for supplying a purge gas to at least the substrate table and / or at least part of the table that is part of the patterning means, wherein the purge gas is substantially incapable of absorbing the projection beam of radiation It is possible to provide a lithographic apparatus having a refractive index at a wavelength λ ₁ equal to the refractive index of air measured at substantially the same wavelength, temperature and pressure.

Claims (30)

A radiation system for providing a projection beam of radiation; Patterning means serving to pattern the projection beam according to a predetermined pattern; A substrate table for holding the substrate; And A projection system for imaging the patterned beam on the target area of the substrate, Interferometer displacement measuring means operating at wavelength λ ₁ for measuring the position of the substrate table or the position of the table which is part of the patterning means; -Further comprising flushing gas means for supplying a purge gas to displace ambient air therefrom in at least a portion of the substrate table and / or in a predetermined space containing at least a portion of the table, wherein the purge gas And a refractive index at a wavelength [lambda] _{1 that} is substantially nonabsorbable to said radiation projection beam and is equal to the refractive index of air measured at substantially the same wavelength, temperature and pressure. The method of claim 1, The purge gas is a lithographic projection apparatus comprising at least two components selected from N ₂ , He, Ar, Kr, Ne, and Xe. A lithographic projection apparatus according to claim 2, wherein said purge gas comprises at least 95% N _{2 by} volume and at least 1% He by volume. The method of claim 2, And said purge gas comprises at least 95% Ar by volume and at least 1% Xe by volume. The method of claim 2, And said purifying gas comprises at least 90% Ar by volume and at least 5% Kr by volume. The method of claim 2, And said purifying gas comprises at least 95% N _{2 by} volume and at least 1% Ne by volume. The method of claim 2, And said purge gas comprises at least 50% N _{2 by} volume and at least 35% Ar by volume. The method of claim 2, And said purge gas comprises at least 94% N _{2 by} volume, at least 0.5% He by volume and at least 0.5% Xe by volume. The method of claim 1, Second harmonic interferometer measuring means operating at wavelengths λ ₂ and λ ₃ to adjust the measurement of the interferometer displacement measuring means to substantially eliminate the effects of pressure and temperature changes, wherein the purge gas Each component comprising at least two different components having refractive properties at wavelengths λ ₂ and λ ₃ , where the following equations are generally satisfied: (Equation 1) (Equation 2) Where F _j is the fraction of component j in the purification gas containing the total number of k elements by volume, α _j1 is the refractive index of component j at wavelength λ ₁ , and α _j2 is the component at wavelength λ ₂ j is the refractive index, 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 , and α _a2 is air at wavelength λ ₂ Is the refractive index of and α _a3 is the refractive index of air at wavelength (λ ₃ ) (Equation 3) Lithographic projection apparatus characterized in that. The method of claim 9, And said purifying gas comprises at least three different components selected from N ₂ , He, Ar, Kr, Ne and Xe. The method of claim 10, The purge gas is (i) N ₂ and / or Ar in an amount of 50% to 90% by volume, (ii) Xe and / or Kr in an amount of 0.5% to 40% by volume and (iii) 2% to 20 by volume A lithographic projection apparatus comprising a% amount of He and / or Ne. A radiation system for providing a projection beam of radiation; Patterning means serving to pattern the projection beam according to a predetermined pattern; A substrate table for holding the substrate; A projection system for imaging the patterned beam on the target area of the substrate, Interferometer displacement measuring means operating at wavelength λ ₁ for measuring the position of the substrate table or the position of the table which is part of the patterning means; Second harmonic interferometer measuring means operating at wavelengths λ ₁ and λ ₂ for adjusting the measurement of the interferometer displacement measuring means to substantially eliminate the effects of pressure and temperature changes; -Flushing gas means for supplying a purge gas to displace ambient air therefrom in a space accommodating at least part of the substrate table and / or at least part of the table that is part of the patterning means, wherein the purge gas Includes at least two components that are substantially nonabsorbing with respect to the projection beam of radiation and each having a refractive index at wavelengths λ ₁ , λ ₂ and λ ₃ such that the following equation is substantially satisfied: (Equation 4) Where α _ml is the refractive index of the purification gas at the wavelength λ ₁ , α _m2 is the refractive index of the purification gas at the wavelength λ ₂ , and α _m3 is the refractive index of the purification gas at the wavelength λ ₃ , (Equation 5) Wherein α _al is the refractive index of the air at the wavelength λ ₁ , and α _a2 and α _a3 are as defined in claim 9. The method of claim 12, And said purifying gas comprises at least two gases selected from N ₂ , He, Ar, Kr, Ne and Xe. The method of claim 13, The purge 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. Lithographic projection apparatus. A radiation system for providing a projection beam of radiation; Patterning means serving to pattern the projection beam according to a predetermined pattern; A substrate table for holding the substrate; A projection system for imaging the patterned beam on the target area of the substrate, Supplying a substantially non-absorbing purge gas to the radiation projection beam for displacing ambient air therefrom in a space containing at least a portion of the substrate table and / or at least a portion of the table that is part of the patterning means. Flushing gas means; Interferometer displacement measuring means operating at a wavelength λ ₁ for measuring the position of the substrate table or the position of the table that is part of the patterning means; And A second harmonic interferometer measuring means operating at wavelengths λ ₂ and λ ₃ for adjusting the measurement of the interferometer displacement measuring means DI according to the following equation, (Equation 9) L = (DI)-K (SHI) Where L is the measured interferometer displacement measuring means, SHI is the measurement of the second harmonic interferometer measuring means and K is a coefficient whose value is optimized to partially remove the effects of pressure, temperature and purge gas composition changes from the adjusted measurement (L) Lithographic projection apparatus characterized in that. The method of claim 15, And said purge gas has a refractive index at a wavelength [lambda] ₁ substantially equal to the refractive index of air measured at the same wavelength, temperature and pressure. The method according to claim 15 or 16, K is given by (Equation 22) Where α _mx and α _ax represent the refractive index of the purification gas or air at wavelength λ _x , respectively, and α _cx is the refraction of the air contaminated by the relative amount c of the purification gas at wavelength λ _x . Wherein _ρ represents phase pressure divided by absolute temperature, σ _ρ is the standard deviation of ρ, and σ _c is the standard deviation of c. The method according to any one of claims 15 to 17, And said purge gas comprises at least 95% of He by volume. The method according to any one of claims 15 to 17, And said purge gas comprises 94% to 96% N _{2 by} volume and 4% to 6% He by volume. The method according to any one of claims 1 to 19, Lithographic projection apparatus characterized in that λ ₁ is approximately 633 nm, λ ₂ is approximately 532 nm and λ ₃ is approximately 266 nm. The method according to any one of claims 1 to 20, The flushing gas means includes a purge gas source as defined in any of claims 1 to 20, a gas flow regulator for controlling the flow rate of purge gas in the space, and an exhaust to remove the purge gas from the space. Lithographic projection apparatus comprising means. A lithographic projection apparatus according to claim 21, wherein said flow regulator comprises a flow restrictor. The method of claim 21 or 22, And said flow regulator comprises a blower. The method according to any one of claims 1 to 23, And said radiation of said projection beam has a wavelength less than about 180 nm, preferably about 157 nm or 126 nm. Providing a substrate at least partially applied by a layer of radiation sensing material; Providing a projection beam of radiation using a radiation system; Using patterning means for imparting a cross-sectional pattern to the excited projection beam; Projecting a patterned beam of radiation onto a target area of the layer of radiation sensing material, Determining the position of a table suitable for supporting the substrate or forming part of the patterning means using interferometric displacement measuring means operating at wavelength λ ₁ ; In a space accommodating at least a portion of the table, a wavelength substantially equal to a reflectance index of air measured at the same wavelength, temperature and pressure and substantially non-absorbing with respect to the projection beam of radiation to displace the ambient air therefrom ( and a purifying gas having a refractive index in λ ₁ ). The method of claim 25, Adjusting the measurement of the interferometer displacement measuring means to substantially eliminate the effects of pressure and temperature changes using second harmonic interferometer measuring means operating at wavelengths λ ₂ and λ ₃ ; The purifying gas comprises at least three different components each having a refractive index at wavelengths λ ₂ and λ ₃ , wherein each component substantially satisfies the following equation, (Equation 1) (Equation 2) Where F _j is a fraction of the volume of component j in the purge gas, the purge gas contains the sum of the k components, α _j1 is the refractive index of component j at wavelength λ ₁ , and α _j2 is the wavelength ( is the refractive index of component j at 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 , and α _a2 is the wavelength ( the refractive index of air at λ ₂ ) and α _a3 is the refractive index of air at wavelength λ ₃ , where: (Equation 3) Device manufacturing method, characterized in that. Providing a substrate at least partially applied by a layer of radiation sensing material; Providing a projection beam of radiation using a radiation system; Using patterning means for imparting a cross-sectional pattern to the projection beam; Projecting a patterned beam of radiation onto a target area of the layer of radiation sensing material, Determining the position of a table suitable for supporting the substrate or forming part of the patterning means using interferometric displacement measuring means operating at wavelength λ ₁ ; Adjusting the measurement of the interferometer displacement measuring means to substantially eliminate the effects of pressure and temperature changes using second harmonic interferometer measuring means operating at wavelengths λ ₂ and λ ₃ ; In a space accommodating at least a portion of the table, wavelengths λ ₁ , λ ₂ and λ ₃ which are substantially nonabsorbing with respect to the projection beam of radiation in order to displace the ambient air therefrom, with each component generally satisfying the following equation: Supplying a purge gas comprising at least two components having refractive properties in (Equation 4) Where α _ml is the refractive index of the purification gas at the wavelength λ ₁ , α _m2 is the refractive index of the purification gas at the wavelength λ ₂ , and α _m3 is the refractive index of the purification gas at the wavelength λ ₃ , (Equation 5) Wherein α _al 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 . Device manufacturing method. (Equation 9) L = (DI)-K (SHI) Where L is the adjusted interferometer displacement measuring means, SHI is the measurement of the second harmonic interferometer measuring means and from the adjusted measurement L the effect of pressure, temperature and purge gas composition changes is partially removed and K is the coefficient . Providing a substrate at least partially coated by a layer of radiation sensing material; Providing a projection beam of radiation using a radiation system; Using patterning means for imparting the cross-sectional pattern to the projection beam; Projecting a patterned beam of radiation onto a target area of the layer of radiation sensing material, Forming in the space containing at least a portion of the table a part of the patterning means suitable for supporting the substrate which is substantially nonabsorbing with respect to the radiation projection beam to displace ambient air therefrom; Determining the position of the table using interferometric displacement measuring means operating at wavelength λ ₁ ; And Adjusting the measurement of said interferometer displacement measuring means using a second harmonic interferometer measuring means operating at wavelengths λ ₂ and λ ₃ according to the following equation, (Equation 9) L = (DI)-K (SHI) Where L is the measured interferometer displacement measuring means, SHI is the measurement of the second harmonic interferometer measuring means and K is a coefficient whose value is optimized to partially remove the effects of pressure, temperature and purge gas composition changes from the adjusted value (L) Device manufacturing method characterized by the above-mentioned. 29. A device made according to any one of claims 25 to 28. 20. Purification gas as defined in any of claims 3, 8, 11, 14, 18 or 19.