Patent Application
20100002209
1. Field of the Invention
The present invention relates to an exposure apparatus and a method of manufacturing a device.
2. Description of the Related Art
In a photolithography process for manufacturing a semiconductor element, a liquid crystal display element, or the like, a circuit pattern with a fine line width formed on a reticle or the like is projected/exposed on a photosensitive substrate such as a wafer coated with a resist layer using a projection exposure apparatus having a high resolving power.
In this projection/exposure step, a volatile substance produced from a photosensitive resin used for a resist layer applied to the wafer adheres to the surface of an optical member of a projection optical system, thus contaminating the optical member surface. For this reason, the operator of a projection exposure apparatus needs to perform wiping operation, that is, cleaning operation, on the optical member surface of the projection optical system. With regard to the execution timing of the above cleaning operation, the operator performs it when visually recognizing the contaminated state or periodically performs it at a predetermined constant periodic timing.
Recently, with increasing miniaturization of semiconductor integrated circuits, the line width uniformity of a transferred pattern is used in a semiconductor exposure apparatus. As a factor that degrades the line width uniformity, the influence of flare occurring in a projection optical system and an illumination optical system has become no longer negligible. The flare occurring in the projection optical system and the illumination optical system makes the illuminance distribution within the exposure screen nonuniform to cause nonuniformity in the line width of an optical image within the screen. When a portion outside the exposure screen is irradiated with flare, nonuniformity occurs in the line widths of optical images in adjacent shots. Flare occurs in the projection optical system and the illumination optical system when the reflectance of the surface of an optical element increases due to contamination or the like on the optical element surface.
Conventionally, flare in the projection optical system and the illumination optical system is estimated from an exposure result on a wafer coated with a resist. For example, the amount of flare occurring in the entire projection optical system and illumination optical system is predicted from a change in the line width of a pattern image exposed by the semiconductor exposure apparatus or a change in the amount of resist film residue outside an exposure region which remains after exposure is performed in a plurality of shots while changing the exposure amount.
Japanese Patent Laid-Open No. 11-283903 proposes a measurement unit which automatically measures contamination on the surface of an optical element in a projection optical system. Japanese Patent Laid-Open No. 11-283903 discloses a measurement unit which automatically measures the reflectance of the surface of an optical element which is closest to a photosensitive substrate, and a photo-cleaning unit which automatically removes contamination on the surface of the optical element which is closest to the photosensitive substrate.
According to the technique described in Japanese Patent Laid-Open No. 11-283903, a measuring light beam is made obliquely incident on the surface of the optical element on the photosensitive substrate side from outside the projection optical system and the illumination optical system without passing through these systems, and the amount of reflected light of the measuring light beam is measured. Therefore, it is difficult to measure the reflectance on the surface of an inner optical element of the illumination optical system. As described above, according to the prior art, it is difficult to measure an increase in flare in each of the optical elements constituting the illumination optical system.
According to the technique described in Japanese Patent Laid-Open No. 11-283903, a light source is additionally provided between the projection optical system and the photosensitive substrate to implement the measurement unit which automatically performs measurement. This complicates the arrangement of the exposure apparatus.
According to an aspect of the present invention, there is provided an exposure apparatus, which project a reticle pattern onto a substrate and exposes the substrate, comprising an optical system configured to illuminate the reticle, including an imaging optical system having an optical element, a reflecting surface which reflects light toward the optical element, and a processor which extracts information from a first signal based on first light which is incident on the imaging optical system and reflected by the reflecting surface and a surface of the optical element, and information from a second signal based on second light which is incident on the imaging optical system and is not reflected by the reflecting surface and the surface of the optical element, and which obtains information indicating a surface condition of the optical element using the information extracted from the first and second signals.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
A first embodiment of an exposure apparatus according to the present invention will be described with reference to
Light from the light source 22 illuminates a reticle placed on a reticle stage 6 via the illumination optical system 21 with an illumination mode (effective light source shape), a polarization state, and an illuminance distribution. The illumination optical system 21 further includes an optical system 213 which forms an effective light source, a Koehler illumination optical system 211, and an imaging illumination optical system 212. A variable aperture masking blade 214 is placed at or near a position which is optically conjugate with the reticle through the imaging illumination optical system 212. The masking blade 214 can limit the illumination range on the reticle within a region. An exposure amount sensor 4′ to control the exposure amount of the illumination system 2 is placed between the light source 22 and the imaging illumination optical system 212. The exposure amount sensor 4′ forms a second sensor which detects the amount of light incident on the imaging illumination optical system 212.
A pattern is formed on the lower surface of the reticle. Diffracted light from this pattern is projected, via a projection optical system 1, on a resist-coated substrate 51 placed on a substrate stage 5 which supports a substrate, thus transferring the pattern onto the substrate 51. In general, at least one of the object plane side and image plane side of the projection optical system 1 used for the exposure apparatus serves as a telecentric optical system. Making the image plane side telecentric, in particular, can theoretically eliminate a change in imaging magnification when the focus is adjusted by changing the level of the substrate. If the object plane (reticle) side of the projection optical system 1 is made telecentric, the image plane (reticle) side of the illumination optical system 21 is also telecentric. A substrate such as a wafer or glass plate will be referred to as “a wafer” hereinafter. Optical elements 11 and 12 are respectively positioned at the wafer side and the reticle side of the projection optical system 1.
Inner optical elements constituting the projection optical system 1 and the illumination system 2 are purged with a gas such as clean dry air or inert gas that does not contain any contaminants, so the surfaces of the optical elements are not easily contaminated. The outermost surfaces of the optical system which form the object plane (reticle) side and image plane side of the projection optical system 1 are respectively in contact with the space where driving mechanisms such as a reticle stage 6 and the substrate stage 5 are present. Likewise, the outermost surface of the optical system which forms the image plane (reticle) side of the illumination optical system 21 is also in contact with the space where a driving mechanism such as the reticle stage 6 is present.
The space where the reticle stage 6 and the substrate stage 5 are present cannot be completely free from contaminants in the atmosphere due to the presence of the driving mechanisms. For this reason, the surfaces of the optical elements of the projection optical system 1 and illumination system 2 which are in contact with this space are easily affected by contamination. Therefore, the outermost surfaces of the optical system which form the object plane side and image plane side of the projection optical system 1 are configured to be replaced as needed. Likewise, the outermost surface of the optical system which forms the image plane (reticle) side of the illumination optical system 21 is configured to be replaced as needed. Replaceably providing optical elements most susceptible to contamination in this manner can keep the optical performance of the illumination optical system 21 constant for a long period of time.
A scanning type semiconductor exposure apparatus performs pattern transfer while synchronously scanning the reticle stage 6 and the substrate 51. A reticle transport system and a wafer transport system (neither is shown) load and unload a reticle and the wafer 51 in and from the exposure apparatus, respectively. The reticle and the wafer 51 loaded by the corresponding transport systems are chucked and fixed on the reticle stage 6 and a wafer chuck 52, respectively.
The reticle stage 6 can be driven in the scanning direction (a direction perpendicular to the drawing surface of each of
Measurement of a surface reflectance as information representing the surface condition of a reticle side optical element 201 of the illumination optical system 21 will be described next. In each of the states shown in
Measurement of the reflectance of the surface of an optical element in the state in
A monopole effective light source is formed by the optical system 213 forming an effective light source. The monopole obliquely incident light beam formed via the Koehler illumination optical system 211 illuminates a reflecting surface 301 formed on a test reticle 3 via the imaging illumination optical system 212. The reflecting surface 301 is formed on the surface of the test reticle 3 which is located on the projection optical system side. This embodiment exemplifies a case in which the reflecting surface 301 is placed on or near the image plane of the illumination optical system 21. Providing the reflecting surface 301 at a position where no contamination occurs in this manner can minimize changes in the reflectance of the reflecting surface 301.
A monopole obliquely incident light beam is formed by providing an effective light source stop 2132 on the exit surface of an integrator such as a fly-eye lens 2131 in the optical system 213 forming an effective light source and extracting a light beam from part of the effective light source. At this time, the exit surface of the integrator such as the fly-eye lens 2131 is optically a pupil plane relative to the reticle plane. By using a switching mechanism for a plurality of stops in a turret form or a variable aperture driving stop mechanism as the effective light source stop 2132, part of an effective light source can be extracted.
The surface reflectance of the optical element 201 which is a measurement target is as low as about 0.1 to 0.2%. In order to measure the surface reflectance of the optical element 201, therefore, it can be done to form an effective light source with a σ value of about 0.1 at the position of the effective light source stop 2132 by using a diffraction optical element such as a computer generated hologram (CGH). This makes it possible to form an obliquely incident light beam with a light amount exhibiting an illuminance several ten times higher than that obtained when monopole illumination light is extracted from a general uniform illumination with a σ value of about 0.8. Since this makes it possible to detect a light amount with a high S/N ratio, a reflectance can be measured with high accuracy.
The light beam exiting from the effective light source stop 2132 Koehler-illuminates a given surface of the masking blade 214, which is a variable aperture stop, via the Koehler illumination optical system 211 formed by a collimator 2111 constituted by a plurality of optical elements. At this time, a given surface of the masking blade 214 is illuminated with an obliquely incident light beam by placing the effective light source stop 2132 at a position eccentric to the optical axis of the collimator 2111.
The masking blade 214 transmits only a light beam in part of the region Koehler-irradiated by the collimator 2111. The light beam passing through the masking blade 214 is deflected by a bending mirror 2122 via a front group 2121 of the imaging illumination optical system, passes through a rear group 2123 of the imaging illumination optical system, and is focused on the reflecting surface 301 of the test reticle 3.
The front group 2121 of the imaging illumination optical system, the bending mirror 2122, and the rear group 2123 of the imaging illumination optical system constitute the imaging illumination optical system 212. The imaging illumination optical system 212 forms an aperture image of the masking blade 214 on the reflecting surface 301 of the test reticle 3. For the sake of simplicity, the following description will be made under the assumption that the imaging magnification of the imaging illumination optical system 212 is 1:1 magnification.
The light beam focused on and reflected by the reflecting surface 301 of the test reticle 3 is reflected by the surface of the reticle side optical element 201 located on the outermost side of the rear group 2123 of the imaging illumination optical system, and passes through the test reticle 3. This light beam then enters the projection optical system 1. The light beam which has entered the projection optical system 1 passes through a light-receiving aperture 41 of the wafer side light amount sensor 4 mounted on the substrate stage 5, and is received by the wafer side light amount sensor 4 to be photoelectrically converted. The wafer side light amount sensor 4 forms a first sensor which detects the light which is incident on the imaging illumination optical system 212 and emitted by the imaging illumination optical system 212.
At this time, the position of the substrate stage 5 at which an obliquely incident light beam enters a light-receiving aperture 41 is calculated in advance, and the substrate stage 5 is driven to the position in advance. The position at which the obliquely incident light beam enters the light-receiving aperture 41 can be obtained by calculating a so-called light beam trace from the following five pieces of information:
A person skilled in the art can easily perform this calculation by automatic calculation using a computer in the projection exposure apparatus.
The reticle side optical element 201 placed on the outermost side of the rear group 2123 of the imaging illumination optical system is often a transmissive element such as an easily replaceable plane-parallel plate.
Measurement of the reflectance of the optical element in the state in
The illuminance of the light beam which illuminates the masking blade 214 is the value of K-IN(1a) obtained by multiplying the light amount IN(1a) measured by the exposure amount sensor 4′ provided in the illumination system by a measurement efficiency K determined by the position of the exposure amount sensor 4′ in the illumination system.
Letting IT be the transmittance of the imaging illumination optical system 212, the illuminance of a light beam illuminating the test reticle 3 is the value given by K-IT-IN(1a).
Letting GT be the transmittance of the glass surface of the test reticle 3, CDR be the reflectance of the reflecting surface 301 of the test reticle 3, and ILLR be the reflectance of the reticle side optical element 201, the illuminance of the light beam reflected by the reflecting surface 301 of the test reticle 3 and the reticle side optical element 201 immediately after passing through the test reticle 3 is given by
K·IT·IN(1a)·(GT4)·CDR·ILLR
The imaging magnification of the projection optical system 1 mounted in the exposure apparatus is generally a reduction magnification of 1/4 or 1/5 or the like. For the sake of simplicity, the following description will be made under the assumption that the projection optical system 1 has an imaging magnification of 1×. A discussion on the case of a reduction magnification of 1/β is apparent, and hence will be omitted.
When the light amount distribution of the light beam immediately after passing through a transmissive aperture formed by the masking blade 214 exhibits uniform light intensity, the light amount distribution of the light beam focused (imaged) on the reflecting surface 301 of the test reticle 3 also exhibits uniform light intensity.
However, in a state in which the light beam reflected by the reflecting surface 301 of the test reticle 3 and the surface of the reticle side optical element 201 has reached the wafer side light amount sensor 4 via the projection optical system 1, the light amount distribution of the light beam which irradiates the light-receiving aperture 41 does not exhibit uniform light intensity. This is because the image of the transmissive aperture formed by the masking blade 214 is defocused on the wafer side light amount sensor 4.
If the light intensity distribution at the imaging position is uniform, the light intensity distribution in the defocused state appears such that the light amount distribution widens due to blurring of an image accompanying an increase in defocus amount, and the light intensity decreases from the peripheral portion of the image. The decrease in light intensity at the peripheral portion of the image due to the blurring of the image is determined by the defocus amount and the light beam diffusion (NA) of the illumination light beam, and can be easily obtained by performing light beam trace in the imaging illumination optical system 212 and the projection optical system 1 in consideration of the light beam diffusion (NA) of the illumination light beam. Therefore, by setting the diameter of the transmissive aperture formed by the masking blade 214 to be larger by the defocus amount of this image in advance, the light amount distribution of the light beam which irradiates the light-receiving aperture 41 can have a uniform distribution in the aperture portion of the light-receiving aperture 41.
When the transmissive aperture formed by the masking blade 214 is set to have a large diameter in this manner, the illuminance of the light beam which enters the light-receiving aperture 41 on the wafer side light amount sensor 4 is expressed by
K·IT·IN(1a)·(GT4)·CDR·ILLR·PT
where PT is the transmittance of the projection optical system 1.
Letting WT be the transmittance of the light-receiving aperture 41, the illuminance of the light beam immediately after passing through the light-receiving aperture 41 is given by
K·IT·IN(1a)·(GT4)·CDR·ILLR·PT·WT
Assume that the wafer side light amount sensor 4 photoelectrically converts a light beam passing through the light-receiving aperture 41. Letting WK be the photoelectric conversion efficiency of the wafer side light amount sensor 4, the light amount OUT(1a) measured by the wafer side light amount sensor 4 is expressed as
OUT(1a)=K·IT·IN(1a)·(GT4)·CDR·ILLR·PT·WT·WK
The surface reflectance ILLR of the reticle side optical element 201 is obtained by solving
ILLR={OUT(1a)/IN(1a)}/{K·(GT4)·IT·PT·CDR·WT·WK}
The following constant terms are obtained to the apparatus in advance: {K·GT4}·IT·PT·CDR·WT·WK}
Of these constant terms, the characteristics of the following five terms can be measured in the respective unit states before the units are built in the exposure apparatus:
These constant terms indicate different values depending on the incident angle of a light beam. Therefore, the optical characteristics are measured in the respective units at different incident angles. A lot of labor is consumed to implement such a measurement environment. Assume that these characteristics are obtained in advance. Even in this case, if the characteristics have changed with time as the units are built in the apparatus and used for a long period of time, the change with time in constant terms directly affects the reliability of the measurement value of the surface reflectance ILLR of the reticle side optical element 201.
It is therefore not advisable to obtain ILLR from the equation obtained in the state in
Measurement in the state in
Measurement in
OUT(1b)=K·IT·IN(1b)·(GT2)·PT·WT·WK
When the surface reflectance ILLR of the reticle side optical element 201 is calculated using two equations (1) and (2) given below which are obtained in the states in
OUT(1a)=K·IT·IN(1a)−(GT4)·CDR·ILLR·PT·WT·WK (1)
OUT(1b)=K·IT·IN(1b)·(GT2)·PT·WT·WK (2)
ILLR={OUT(1a)/IN(1a)/OUT(1b)/IN(1b)}·{1/(GT2·CDR)} (3)
It is possible to obtain the surface reflectance ILLR of the reticle side optical element 201 by using only the four terms described below:
The above technique is very simple because the characteristics unique to the apparatus which should be stored in the exposure apparatus in advance include only the transmittance GT of the glass surface of the test reticle 3 and the reflectance CDR of the reflecting surface 301 of the test reticle 3. That is, it suffices to only actually measure in advance the relationship between the transmittance GT of the glass surface and the reflectance CDR of the reflecting surface 301 of the test reticle 3 and store it in the exposure apparatus in advance.
At this time, it suffices to obtain the relationship among the glass surface transmittance GT, the reflectance CDR of the reflecting surface 301 of the test reticle 3, and the incident angle of measuring light by computation in the exposure apparatus using the optical property value of the glass material of the test reticle 3 and that of the upper surface of the test reticle.
As described above, in this embodiment, that surface of the reflecting layer formed on the lower surface of the test reticle 3 which is located on the illumination optical system 21 side is formed into the reflecting surface 301. Even if, therefore, the test reticle 3 is erroneously contaminated, it does not influence the reflectance CDR of the reflecting surface 301 of the test reticle 3. Since the transmittance GT of the glass surface can be recovered easily by cleaning the test reticle 3 with a cleaning unit, a change with time in constant terms which affects the reliability of the measurement value of ILLR does not occur easily.
As the exposure amount sensor 4′ to measure the light amounts IN(1a) and IN(1b), an exposure amount control sensor generally positioned in the illumination system 2 can be used. Likewise, as the wafer side light amount sensor 4 to measure the light amounts OUT(1a) and OUT(1b), an exposure amount control sensor generally positioned on the substrate stage can be used.
As described above, a simple arrangement using only the test reticle 3 provided with the reflecting surface 301 for a generally used exposure apparatus can measure the surface reflectance of the optical element 201 based on the detection results obtained by the wafer side light amount sensor 4 and the exposure amount sensor 4′.
The light which is incident on the imaging illumination optical system 212 and reflected by the reflecting surface 301 and the surface of the optical element 201 in the state in
The above description is made under the assumption that the following two values are equal to each other in the states in
Strictly speaking, however, these values are equivalent only when the object (reticle) plane side of the projection optical system 1 and the image (reticle) plane side of the imaging illumination optical system 212 are nearly telecentric, and the outermost optical element 201 on the image (reticle) plane side, which is a reflectance measurement target, is a flat surface. Only under these conditions, it is possible to measure the surface reflectance of the reticle side optical element 201 in the imaging illumination optical system 212 without being influenced by the angular characteristics (the sensor output changes depending on the incident angle of a light beam on the sensor) of the sensitivity of the light amount sensor.
Even if these conditions are not satisfied, there is no issue when monitoring (repeating measurement every specific period of time) a change with time in the surface reflectance of the reticle side optical element 201 in the imaging illumination optical system 212.
In this case, approximation is made such that both the following two values are equal to each other in the states in
In step S4, the processor P drives the reticle stage 6 to match the reflecting surface 301 of the test reticle 3 with the image height in the imaging illumination optical system 212 which is to be measured. In step S5, the processor P sets an illumination region. The processor P drives the masking blade in the illumination system 2 to illuminate only a portion near the reflecting surface 301 of the test reticle 3 corresponding to the image height to be measured. In step S6, the processor P drives the substrate stage 5 to be set in the state in
In step S7, the processor P oscillates a light source laser or the like to irradiate the test reticle 3 with the illumination light. In step S8, the exposure amount sensor 4′ positioned in the illumination system 2 and the wafer side light amount sensor 4 positioned on the substrate stage 5 simultaneously measure the light amounts OUT(1a) and IN(1a). In step S9, the processor P stops oscillation of the light source laser or the like so as not to irradiate the test reticle 3 with illumination light.
In steps S10 and S11, the processor P drives the reticle stage 6 and the substrate stage 5 to set the state in
In step S14, for example, the processor P stops oscillation of the light source laser so as not to irradiate the test reticle 3 with illumination light.
In step S15, the processor P calculates the reflectance ILLR from the measurement values OUT(1b), IN(1b), OUT(1a), and IN(1a) and the incident angle characteristic values of the reflectance CDR of the reflecting surface 301 and of the transmittance GT of the glass surface of the test reticle 3 in consideration of the incident angle at the time of measurement. Note that as the incident angle characteristic values of the reflectance CDR of the reflecting surface 301 and of the transmittance GT of the glass surface of the test reticle 3, data stored in the exposure apparatus in advance can be used.
A second embodiment of the present invention will be described below referring to the drawings. Measurement of the reflectance of an optical element 202 in an illumination optical system 21 will be described with reference to
Measurement in the state in
Referring to
The light beam entering the projection optical system 1 passes through a light-receiving aperture 41 of the wafer side light amount sensor 4 placed on the substrate stage 5, and is received by the wafer side light amount sensor 4 to be photoelectrically converted. At this time, the position of a light beam passing through the projection optical system 1 differs between the state in
Measurement in the state in
Letting T2123 be the transmittance of the rear group 2123 of the imaging illumination optical system, R2122 be the reflectance of the bending mirror 2122, and R202 be the reflectance of the optical element 202, the light amount in a state in which the light beam reflected by the surface of the optical element 202 has entered the test reticle 3 again and has passed through it is given by
K·IT·IN(2a)·(GT4)·(T21232)·(R21222)·R202·CDR
The light amount OUT(2a) on the wafer side in the state in
OUT(2a)=K·IT·IN(2a)·(GT4)·(T21232)·(R21222)·R202·CDR·PT·WT·WK
Measurement in the state in
OUT(2b)=K·IT·IN(2b)·(GT2)·PT·WT·WK
The equations for OUT(2a) and OUT(2b) yield
R202·(T21232)·(R21222)={OUT(2a)/IN(2a)/OUT(2b)/IN(2b)}·{1/(CDR·GT2)}
In addition, regarding T2123≈1 and R2122≈1 yields
R202≈{OUT(2a)/IN(2a)/OUT(2b)/IN(2b)}·{1/(CDR·GT2)}
With approximations of T2123≈1 and R2122≈1, there is no issue when monitoring (repeating measurement every specific period of time) a change with time in the surface reflectance R202 of the optical element 202.
In this manner, the surface reflectance R202 of the optical element 202 can also be obtained by using the same equation as that used for the surface reflectance ILLR of the optical element 201 shown in the first embodiment.
A third embodiment configured to measure the reflectance of an optical element 203 in an illumination optical system 21 will be described with reference to
Measurement in the state in
The light beam passing through the front group 2121 of the imaging illumination optical system is deflected by a bending mirror 2122 and passes through a rear group 2123 of the imaging illumination optical system. This light beam further passes through a test reticle 3 and enters a projection optical system 1. The light beam entering the projection optical system 1 passes through a light-receiving aperture 41 of a wafer side light amount sensor 4 placed on a substrate stage 5 and is received by the wafer side light amount sensor 4 to be photoelectrically converted. The position of a light beam passing through the projection optical system 1 differs between the states in
Measurement in the state in
The reflectance of the masking blade 214 is represented by R214. The light amount in a state in which the light beam reflected by the surface of the optical element 203 has been reflected by the masking blade 214 and has entered and passed through the test reticle 3 via the imaging illumination optical system 212 is given by
K·IN(3a)·R203·R214·IT·(GT2)
The light amount OUT(3a) on the wafer side in the state in
OUT(3a)=K·IN(3a)·R203·R214·IT·(GT2)·PT·WT·WK
Measurement in the state in
OUT(3b)=K·IT·IN(3b)·(GT2)·PT·WT·WK
Solving equations (4) and (5) for the light amounts OUT(3a) and OUT(3b) on the wafer side in the states in
OUT(3a)=K·IT·IN(3a)·(GT2)·R203·R214·PT·WT·WK (4)
OUT(3b)=K·IT·IN(3b)·(GT2)·PT·WT·WK (5)
R203={OUT(3a)/IN(3a)/OUT(1b)/IN(1b)}·{1/(R214)} (6)
In this case, the relationship between the reflectance R214 of the glass surface of the masking blade 214 and the incident angle of measuring light is actually measured and stored in the exposure apparatus in advance.
The relationship between the second and third embodiments will be described next.
In the second embodiment, the reflectance of the surface of the optical element 202 in the front group 2121 of the imaging illumination optical system is obtained by
R202·(T21232)·(R21222)={OUT(2a)/IN(2a)/OUT(2b)/IN(2b)}·{1/(CDR·GT2)}
The method in the third embodiment obtains the same reflectance of the surface of the optical element 202 according to
R202·(T2121)={OUT(3a)/IN(3a)/OUT(1b)/IN(1b)}·{1/(R214)}
where T2121 is the transmittance of the front group 2121 of the imaging illumination optical system.
Regarding that T2123≈1, R2122≈1, and T2121≈1, the above two equations are expressed as follows.
(Technique in Second Embodiment)
R202={OUT(2a)/IN(2a)/OUT(2b)/IN(2b)}{1/(CDR·GT2)}
(Technique in Third Embodiment)
R202·(T2121)={OUT(3a)/IN(3a)/OUT(1b)/IN(1b)}{1/(R214)}
As described above, it is possible to obtain the reflectance of the optical element 202 in the imaging illumination optical system 212 by using either the technique in the second embodiment or the technique in the third embodiment.
It suffices to determine which one of the techniques is to be selected, from the following two points based on the design data of the lenses of the imaging illumination optical system 212 and projection optical system 1:
Obviously, the technique that should be selected is a technique exhibiting a large amount of light received and a high degree of separation from reflected measuring light from another surface.
A fourth embodiment of the present invention will be described below referring to the drawings.
First of all, letting θ1 be the initial set value of the incident angle of illumination light, a reflectance ILLR(θ1) at the incident angle θ1 of illumination light is calculated. Since the details of the calculation of ILLR are the same as those in
A case in which the incident angle of illumination light is changed to θ2 will be described next. When the incident angle is to be set to θ2, it is not necessary to newly drive a reticle stage 6 or set an illumination region, but it suffices to set the same state as that set for the incident angle θ1. However, the driving position of a substrate stage 5 is set to the substrate stage position (1a, θ2) which is newly calculated for the incident angle θ2.
In the state of the substrate stage position 1a(θ2), light amounts OUT(1a, θ2) and IN(1a, θ2) are simultaneously measured. The substrate stage 5 is driven to the substrate stage position (1b, θ2) newly calculated for the incident angle θ2. In this state, light amounts OUT(1b, θ2) and IN(1b, θ2) are simultaneously measured.
A reflectance ILLR(θ2) at the incident angle θ2 of illumination light is calculated by using the measurement values OUT(1a, θ2), IN(1a, θ2), OUT(1b, θ2), and IN(1b, θ2).
Subsequently, measurement is performed up to an incident angle θn of illumination light in the same manner as described above, and a reflectance ILLR(θn) at the incident angle θn of illumination light is calculated.
In this manner, it is possible to measure the surface reflectances ILLR(θ1) to ILLR(θn) of the optical element at the incident angles θ1 to θn of illumination light. Based on changes in surface reflectances ILLR(θ1) to ILLR(θn) at the incident angles θ1 to θn, it is possible to estimate optical property values such as the refractive index and thickness of a contaminant adhering to the surface of the optical element.
It is noted that steps S1 to S3, S6 to S9, and S11 to S15 of
In the first to fourth embodiments, the exposure amount sensor 4′ in the illumination system 2 measures the light amounts In(1a) and In(1b) and the like. If, however, the light source can emit an almost constant amount of light, the light amounts In(1a) and In(1b) need not be measured. If the light source emits an almost constant amount of light, IN(1a)≈IN(1b).
In the first to fourth embodiments, for example, it suffices to perform measurement while adjusting the amount of light emitted from the light source to set OUT(1a)≈OUT(1b). This makes it possible to minimize the influences of a decrease in S/N ratio of both OUT(1a) and OUT(1b) due to electrical noise in the wafer side light amount sensor 4. In this case, the light amounts measured by the exposure amount sensor 4′ in the illumination system 2 satisfy IN(1a)<IN(1b).
The first to fourth embodiments each have exemplified the case in which a reflectance is measured by the wafer side light amount sensor 4 formed on the substrate stage 5. However, the arrangement of the wafer side light amount sensor 4 is not limited to that fixed on the substrate stage 5. For example, it suffices to use an arrangement including a measurement unit such as a light amount sensor, a power supply, and a communication device on a circular plane-parallel plate having the same shape as that of the wafer 51. In this case, a light amount measurement result is transmitted to the main body of the exposure apparatus by wireless communication.
The third and fourth embodiments each have exemplified the case in which a reflectance is measured by the wafer side light amount sensor 4 formed on the substrate stage 5. However, it suffices to form a light amount sensor on the reticle stage 6 instead of the wafer side light amount sensor 4. It also suffices to use an arrangement including a measurement unit such as a light amount sensor 4, a power supply, and a communication device on a rectangular plane-parallel plate having the same shape as that of the test reticle 3. In this case, a light amount measurement result is transmitted to the main body of the exposure apparatus by wireless communication.
In each of the first and second embodiments, it suffices to use an arrangement including a measurement unit such as a light amount sensor, a power supply, and a communication device on a rectangular plane-parallel plate having the same shape as that of the test reticle 3 instead of the wafer side light amount sensor 4. In this case, a light amount receiving aperture and a reflecting surface are formed on the upper surface of a circular plane-parallel plate, and a light amount measurement result is transmitted to the main body of the exposure apparatus by wireless communication.
An example of a method of manufacturing a device such as a semiconductor integrated circuit element or a liquid crystal display element using the exposure apparatus described above will be described.
Devices are manufactured by a step of transferring by exposure a pattern onto a substrate using the exposure apparatus described above, a step of developing the substrate exposed in the exposing step, and other known steps (e.g., etching, resist removing, dicing, bonding, and packaging steps) of processing the substrate developed in the developing step.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2008-177404, filed Jul. 7, 2008, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-177404 | Jul 2008 | JP | national |
