JPH0729802A - Projection aligner - Google Patents

Abstract

PURPOSE:To project the pattern image of a reticle onto a wafer constantly under predetermined imaging conditions regardless of the presence or absence of pellicle and the like. CONSTITUTION:Pellicle decision units 24, 25 or a bar code reader 27 makes a decision whether pellicles 28, 29 are loaded to a reticle R and delivers the decision results to a main controller 26. The main controller 26 calculates thermal deformation of the reticle R depending on the presence or absence of the pellicles 28, 29 and then calculates a variation, e.g. the magnification of image projected onto a wafer W, based on the thermal deformation thus calculated. The magnification of a projection optical system PL is then corrected through a drive element control section 23 such that the variation thus calculated, e.g. the magnification, is offset.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is for projecting and exposing a pattern of a reticle onto a photosensitive substrate when a semiconductor integrated circuit, a thin film magnetic head, a liquid crystal display device or the like is manufactured by a photolithography process. The present invention is particularly effective when applied to a projection exposure apparatus used when a reticle is provided with a dust-proof film (pellicle).

[0002]

2. Description of the Related Art When manufacturing a semiconductor integrated circuit, a thin film magnetic head, a liquid crystal display device or the like in a photolithography process, a photomask or a reticle (hereinafter referred to as a "reticle") is exposed to light from an illumination optical system. (Collectively)
There is used a projection exposure apparatus that exposes an image of the pattern of (1) on a substrate (wafer, glass plate, etc.) coated with a photoresist via a projection optical system. In this type of projection exposure apparatus, in order to form a semiconductor integrated circuit or the like on a substrate with high accuracy, the imaging characteristics of the projection optical system (for example, magnification, focus position, etc.) are always maintained in a predetermined state, It is necessary to project and expose the pattern image of the reticle onto the substrate.

In this regard, the reticle or the projection optical system absorbs the exposure light during exposure, so that the lens element or the like in the reticle or the projection optical system undergoes thermal deformation or the like,
As a result, even when the imaging characteristics change, the yield of the finally obtained semiconductor integrated circuit or the like decreases. Therefore, conventionally, there has been proposed a method of correcting a change in the imaging characteristic due to absorption of exposure light of a reticle or a projection optical system. First, regarding the absorption of exposure light of the projection optical system, for example, JP-A-60-78455 or JP-A-63-583.
Japanese Patent Publication No. 49 discloses a projection exposure apparatus including a mechanism that detects the amount of light incident on the projection optical system and corrects fluctuations in the optical characteristics of the projection optical system. Regarding the absorption of exposure light by the reticle, for example, Japanese Patent Laid-Open No. 4-192317.
In the publication, a mechanism is disclosed in which the amount of thermal deformation of the reticle is calculated and the optical characteristics of the projection optical system are corrected according to the calculation result.

Usually, in the thermal deformation of the reticle, the light shielding member (usually a metal film such as chromium) of the circuit pattern drawn on the reticle absorbs the exposure light beam, and the glass substrate (usually quartz glass) of the reticle thermally expands. Caused by causing. Therefore, in order to obtain the thermal expansion amount of the reticle by calculation, conventionally, information such as the material of the light shielding member or the absorptance of the exposure light beam, the density distribution (pattern existence rate) of the circuit pattern, the power of the light source, and the like is previously obtained. The calculation was performed using a model corresponding to the variation characteristic of the thermal deformation.

The main changes in the image forming characteristics caused by thermal deformation are magnification changes (due to thermal expansion of the entire reticle),
Or because of distortion (due to distortion and non-uniform thermal expansion of the reticle), conventionally, for example, some lens elements in the projection optical system are moved in the optical axis direction, or
Alternatively, the image forming characteristic of the projection optical system is corrected so as to cancel the change in the image forming characteristic by tilting. Note that the change in magnification in this case includes the case where the size of the circuit pattern exposed on the substrate changes from the designed size due to the thermal expansion of the reticle even when the projection magnification of the projection optical system does not change. It is a concept.

[0006]

In recent years, with the miniaturization of patterns on semiconductor integrated circuits and the like, a decrease in yield due to foreign substances (microscopic dust in the air, etc.) adhering to the patterns on the reticle has become a problem. . Therefore, a protective film (so-called pellicle) is formed on the pattern forming surface or both surfaces of the glass substrate of the reticle via a rectangular frame (pellicle frame).
A method of preventing foreign matter from directly adhering to the circuit pattern is adopted by arranging or arranging a cover glass or the like.

The pellicle and the like form an air chamber which is isolated and sealed from the outside on one or both surfaces of the glass substrate of the reticle as a matter of course. Therefore, when the reticle absorbs the exposure light and the temperature rises, the air in the sealed air chamber serves as a heat insulating material and prevents heat from being transferred from the reticle to the outside. That is, the temperature rise of the reticle becomes large. As a result, even with the same reticle, the state of thermal deformation differs depending on the presence or absence of a pellicle and the like, and there is the inconvenience that the amount of change in the imaging characteristics differs.

The influence of the pellicle and the like is not only the above-described heat insulating effect, but also the amount of deformation of the reticle may be increased due to thermal expansion of the pellicle frame (metal frame) that supports the pellicle and the like. Further, not all reticle used in the same projection exposure apparatus use pellicles and the like, and reticle in which a rough pattern having a relatively small minimum line width is formed is not mounted with pellicles or the like. In some cases. Therefore, the pellicle and the like cannot be uniformly treated as being used.

In view of the above point, an object of the present invention is to provide a projection exposure apparatus that can always maintain a predetermined image formation state regardless of the presence or absence of a pellicle or the like.

[0010]

A projection exposure apparatus according to the present invention is, for example, as shown in FIG. 1, an illumination optical system (1, 5, 5) for illuminating a pattern on a mask (R) with illumination light (IL).
8, 9) and a projection optical system (PL) for exposing the image of the pattern of the mask (R) on the photosensitive substrate (W) in a predetermined image formation state.
In the projection exposure apparatus having the above, data input means (24, 2) for inputting shape data representing the shape of the mask (R).
5, 27, or 36) and the shape data input from the data input means, the calculation means (26) for calculating the change amount of the predetermined image formation state caused according to the thermal deformation amount of the mask (R). ) And image forming state correcting means (12, 13, 19, 23) for correcting the image forming state of the projection optical system (PL) so as to cancel the amount of change calculated by the calculating means. is there.

In this case, an example of the shape data is data indicating the presence / absence of a protective member (pellicle etc.) for preventing foreign matter from adhering to the pattern forming surface of the mask (R) and the thickness of the mask (R). Is. Also, the mask (R)
When a protection member (28 to 31) for preventing foreign matter from adhering to the pattern formation surface is attached to the surface, a temperature measurement for measuring the temperature inside the protection member as shown in FIG. 6, for example. Means (61, 62) are provided, and the calculation means (26) uses the mask (R) based on the temperature information obtained by the temperature measurement means (61, 62) and the shape data input from the data input means. It is desirable to calculate the amount of change in the predetermined image-forming state that occurs according to the amount of thermal deformation in (4).

[0012]

According to the present invention, when the pattern image of the mask (R) is projected and exposed on the photosensitive substrate (W), the shape data of the mask (R) (for example, protection of the pellicle etc.) is first obtained from the data input means. Information about the presence or absence of a film, the temperature inside the protective film such as the pellicle, or the thickness of the glass substrate of the mask)
Is input to the calculating means (26). Using the shape data, the calculation means (26) calculates the thermal deformation amount of the mask (R), and then, based on this thermal deformation amount, the projection image formation state (magnification, focus) on the photosensitive substrate (W). The amount of change in position etc.) is calculated. In accordance with this, the image formation state correction means (12, 1)
3, 19, 23), for example, by changing the position or tilt angle of a predetermined lens in the lens forming the projection optical system (PL) in the optical axis direction, or changing the position or tilt angle of the mask (R) , The image forming state is changed so as to cancel the change amount of the image forming state calculated by the calculating means (26). As a result, the imaging state of the projected image on the photosensitive substrate (W) is maintained in a predetermined state regardless of the presence or absence of a protective film such as a pellicle or the thickness of the glass substrate of the mask (R).

Further, as shown in FIG. 6, for example, temperature measuring means (61, 62) for measuring the temperature inside the protective member such as a pellicle is provided, and the calculating means (26) is operated by the temperature measuring means (61). , 62) based on the temperature information obtained by the measurement and the shape data input from the data input means, the amount of change in the predetermined image formation state that occurs according to the amount of thermal deformation of the mask (R) is calculated. In this case, the amount of change in the image formation state is calculated more accurately, and as a result, the image formation state is maintained more stable in the desired state.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the projection exposure apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 shows the entire structure of the projection exposure apparatus of this example. In FIG. 1, a light source 1 composed of, for example, an ultra-high pressure mercury lamp is an illumination light (i-line or the like) in a wavelength range that exposes a photoresist layer. Generate IL. As the illumination light IL, a laser beam such as a KrF or ArF excimer laser or a harmonic wave of a metal vapor laser or a YAG laser may be used in addition to the bright line of an ultra-high pressure mercury lamp.

Illumination light (exposure light) I emitted from the light source 1
The light L passes through the shutter 2 and the beam splitter 4 having a large transmittance and is incident on the first partial optical system 5 including a fly-eye lens or the like. The shutter 2 closes and opens the optical path of the illumination light IL by the shutter drive system 3. Most of the illumination light passes through the beam splitter 4, and a part of the illumination light reflected by the beam splitter 4 enters the light receiving surface of the photoelectric conversion element 34 (details will be described later).

The first partial optical system 5 is for illuminating the reticle R with a substantially uniform illuminance. The illumination light IL emitted from the first partial optical system 5 passes through the variable reticle blind 6 and then enters the second partial optical system 8 including a relay lens and a main condenser lens. The arrangement surface of the variable reticle blind 6 is in a conjugate relationship with the pattern forming surface of the reticle R, and the driving system 7 drives a plurality of movable blades forming the variable reticle blind 6 to change the size and shape of the opening. , Reticle R
The illumination visual field of can be arbitrarily set. The illumination light IL that has passed through the second partial optical system 8 is bent substantially vertically downward by the mirror 9 and illuminates the reticle R on which the circuit pattern is drawn with a substantially uniform illuminance.

The reticle R is held by a reticle holder 18, and the reticle holder 18 is two-dimensionally arranged in a horizontal plane through a plurality of expandable and contractible (for example, three, only two are shown in FIG. 1) drive elements 19. It is mounted on a reticle stage (not shown) that is movably supported. Drive element 1
An electrostrictive element or a magnetostrictive element is used as 9. The reticle alignment microscope 32 is arranged on the reticle R, and the light from the alignment mark on the reticle R is guided to the image sensor 33 via the reticle alignment microscope 32. The position of the alignment mark is detected using the image pickup signal of the image pickup device 33, and the reticle R is positioned (aligned) based on the detection result. The image pickup signal of the image pickup device 33 is also used to obtain the reflectance of the pattern of the reticle R.

Further, on the upper and lower surfaces of the reticle R, protective films (hereinafter referred to as "pellicle") 28 and 2 for preventing adhesion of foreign matter are provided.
9 are stretched via rectangular frames (hereinafter referred to as “pellicle frames”) 30 and 31. The pellicle frames 30 and 31 are usually made of metal, and when used, they are attached to the glass substrate of the reticle R by an adhesive previously applied to the pellicle frames 30 and 31.

FIG. 2 is a perspective view of the reticle R. As shown in FIG. 2, the space surrounded by the pellicles 28, 29 and the pellicle frames 30, 31 and the glass substrate of the reticle R is located above and below the reticle R. To form a sealed air chamber. Returning to FIG. 1, the drive element control unit 23 controls the expansion and contraction amounts of the drive element 19 so that the reticle R is translated in the direction of the optical axis AX of the projection optical system PL and a plane perpendicular to the optical axis AX. It is possible to incline at an arbitrary angle with respect to. With the above configuration, it is possible to correct the image forming characteristic of the projection optical system PL, particularly the pincushion type or barrel type distortion. Reticle R
Are positioned so that the center point of the pattern area PA coincides with the optical axis AX. Further, the illumination light reflected by the pattern of the reticle R and the illumination light returned from the projection optical system PL side return to the beam splitter 4 via the second partial optical system 8 and the first partial optical system 5, respectively. The light beam reflected by the beam splitter 4 is detected by the photoelectric conversion element 35 (details will be described later).

The illumination light IL which has passed through the pattern area PA of the reticle R is incident on the projection optical system PL which is telecentric on both sides, and the projection optical system PL projects a projected image of the circuit pattern of the reticle R on the surface of which a photoresist layer is formed. The formed (superimposed) image is superposed and projected (imaged) on one shot area on the wafer W held so that its surface substantially coincides with the best imaging plane of the projection optical system PL. In this embodiment, a part of the lens elements forming the projection optical system PL, that is, the lens element 14 and the lens element (1
5, 16) can be independently driven by the drive element control unit 23, and the imaging characteristics of the projection optical system PL, such as projection magnification and distortion, can be corrected (details will be described later). ). A variable aperture stop (not shown) is provided in the pupil plane of the projection optical system PL or in the vicinity thereof, and the numerical aperture NA of the projection optical system PL can be changed by this.

On the other hand, the wafer W is vacuum-sucked on the wafer holder (θ table) 8, and the wafer holder 8 is held on the wafer stage 9. The wafer stage 9 can be tilted in any direction with respect to the best imaging plane of the projection optical system PL by a motor (not shown), can be driven in the optical axis direction (Z direction) of the projection optical system PL, and can be stepped and It is configured to be two-dimensionally movable by the repeat system, and when the transfer exposure of the reticle R to one shot area on the wafer W is completed, the wafer stage 9 is stepped to the next shot position. The wafer stage 9
For the configuration and the like of JP-A-62-274201
It is disclosed in the publication. A movable mirror (not shown) that reflects a laser beam from an interferometer (not shown) is fixed to the end of the wafer stage 9, and the two-dimensional position of the wafer stage 9 is set to, for example, 0 by the interferometer. .01
It is constantly detected with a resolution of about μm.

On the wafer stage 9, a dose monitor 22 composed of a photoelectric conversion element is provided at a height which is substantially equal to the height of the surface of the wafer W. The irradiation amount monitor 22 is composed of, for example, a photoelectric conversion element having a light receiving surface having substantially the same area as the image field of the projection optical system PL or the projection area of the reticle pattern, and the irradiation amount of the illumination light on the wafer stage 9. To the main controller 26. This light information serves as basic data for obtaining the pattern existence rate of the reticle and the variation amount (aberration amount) of the imaging characteristic corresponding to the energy amount accumulated in the projection optical system PL with the incidence of the illumination light. .

Further, in FIG. 1, irradiation optics for supplying an image forming light beam for forming an image of a pinhole or a slit toward the best image forming plane of the projection optical system PL obliquely with respect to the optical axis AX. A grazing incidence type wafer position detection system is provided which includes a system 20 and a light receiving optical system 21 which receives a reflected light beam of the imaged light beam on the surface of the wafer W through a slit. The structure of the wafer position detection system is disclosed in, for example, Japanese Patent Laid-Open No. 60-168112, and a detection signal from the light receiving optical system 21 causes the wafer surface to move in the vertical direction (Z direction) with respect to the best image plane. The position is detected, and based on the detection result, the wafer stage 9 is driven in the Z direction so that the wafer W and the projection optical system PL maintain a predetermined distance.

Further, in this embodiment, the angle of a parallel flat glass (plane parallel) (not shown) provided inside the light receiving optical system 21 in advance is set so that the best image plane of the projection optical system PL becomes the zero point reference. The wafer position detection system is adjusted and calibrated. Further, for example, Japanese Patent Laid-Open No. 58-1
A wafer position detection system is configured to use a horizontal position detection system as disclosed in Japanese Patent No. 13706, or to detect focal positions at arbitrary plural positions within an image field of the projection optical system PL (for example, By projecting a plurality of slit images in the image field), the inclination of a predetermined region on the wafer W with respect to the best image plane can be detected.

Further, in FIG. 1, the main control unit 26 is for performing overall control of the entire apparatus, and the operator controls the main control unit 26 via the console 36 to indicate the presence or absence of the pellicle of the reticle R and the glass substrate of the reticle R. Enter information such as the thickness of the product as needed. A bar code BC representing the name of the reticle formed beside the reticle pattern while the reticle R is being conveyed right above the projection optical system PL.
A bar code reader 27 for reading is read, and information on the name of the reticle read by the bar code reader 27 is supplied to the main controller 26.

Pellicle discriminators 24 and 25 are arranged above and below the reticle holder 18, respectively. The pellicle discriminators 24 and 25 are, for example, non-contact photoelectric sensors or mechanical limit switches, and the pellicle discriminators 24 and 25 are used to detect the reticle R, respectively.
It is actually detected whether the pellicle frames 30, 31 or the pellicles 28, 29 are mounted on the upper and lower surfaces of the. This detection result is also output to main controller 26.
The main controller 26 uses the information input from the console 36,
Based on the information read by the bar code reader 27, the information detected by the pellicle discriminators 24, 25, and the like, the thermal deformation amount of the reticle is calculated as described later.

Next, the means for correcting the image formation state of this embodiment will be described. This correcting means is originally a projection optical system PL that is generated by atmospheric pressure change, temperature change or exposure light absorption.
It is provided for the purpose of correcting the change in the imaging characteristic of itself. In this embodiment, the correction means is used to correct the change in the image forming characteristics caused by the thermal deformation of the reticle. There are various modes of changing the imaging characteristics, but here, only the components considered to be generated by the thermal deformation of the reticle will be described. First, consideration will be given to magnification change ΔM, trapezoidal distortion ΔT, distortion aberration (so-called barrel type or pincushion type distortion) ΔD caused by thermal expansion of the reticle, and field curvature ΔC caused by bending of the reticle.

First, the correction mechanism will be described. As shown in FIG. 1, in the present embodiment, the drive element control unit 23 independently drives each of the reticle R, the lens element 14, and the lens element (15, 16).
It is possible to correct the above-mentioned change in the image forming characteristic. The first group of lens elements 14 closest to the reticle R is fixed to the support member 10, and the second group of lens elements (15, 16) are integrally fixed to the support member 11. The lens elements below the third group of lens elements 17 are fixed to the lens barrel of the projection optical system PL. In the present embodiment, the optical axis AX of the projection optical system PL refers to the optical axis of the lens element fixed to the lens barrel portion.

A plurality of support members 10 (for example, 3
One of them is connected to the supporting member 11 via two driving elements 12 (shown in FIG. 1), and the supporting member 11 is connected to the lens barrel portion via a plurality of expandable and contractable driving elements 13. As the drive elements 19, 12 and 13, for example, an electrostrictive element (piezo element) or a magnetostrictive element is used, and the displacement amount of the drive element according to the voltage or magnetic field applied to the drive element is obtained in advance. Although not shown here, a position detector such as a linear encoder, a capacitive displacement sensor, or a differential transformer is provided in the drive element in consideration of the hysteresis characteristic of the drive element, and it corresponds to the voltage or magnetic field applied to the drive element. The position of the driving element is monitored to enable highly accurate driving.

Here, when each of the lens element 14 and the lens elements (15, 16) is translated in the optical axis direction, the projection magnification M, the field curvature C and the focus position F are changed at a rate corresponding to the amount of movement. Each of the changes. The driving amount of the lens element 14 is x ₁ , the lens element (15,
If the driving amount in 16) is x ₂ , then the projection magnification M, the field curvature C, and the change amounts ΔM, ΔC, and ΔF of the focus position F are
It is expressed by the following equation.

ΔM = C _M1 × x ₁ + C _M2 × x ₂ (1) ΔC = C _C1 × x ₁ + C _C2 × x ₂ (2) ΔF = C _F1 × x ₁ + C _F2 × x ₂ (3) C _M1 , C _M2 , C _C1 , C _C2 , C _F1 , and C _F2 are constants that represent the rate of change of each change amount with respect to the drive amount of the lens element, and ΔF is the change amount of the focal position.

When the lens element 14 is tilted (rotated) so that the straight line perpendicular to the optical axis AX becomes the rotation axis, the trapezoidal distortion ΔT changes. This state is shown in FIG. In FIG. 3, a square pattern QA drawn by a solid line is a projected image of the reticle R, and when the lens element 14 of FIG. 1 is tilted about the axis AX1 shown by a chain line as a rotation axis, for example, a trapezoidal shape drawn by a dotted line. The projected image can be distorted like the pattern QB.

Therefore, the trapezoidal distortion ΔT is determined by the inclination angle θ ₁ of the lens element 14 and the direction of the rotation axis AX1. For convenience of explanation, assuming that the direction of the rotation axis AX1 is fixed in a predetermined direction, the trapezoidal distortion ΔT is calculated using the tilt angle θ ₁ and the rate of change C _T1 with respect to this tilt angle.
Is expressed by the following equation. Also, assuming that the image plane tilt amount in this case is ΔL, the image plane tilt amount ΔL is expressed as follows using the change rate C _T2 .

ΔT = C _T1 θ ₁ (4) ΔL = C _T2 θ ₁ (5) By the way, as described above, the wafer position detecting system 20 of FIG.
Reference numeral 21 is for detecting the amount of deviation of the wafer surface with respect to the optimum focus position, with the position of the best image plane of the projection optical system PL (the optimum focus position) as the zero point reference. Therefore, when an appropriate offset amount x ₃ is applied electrically or optically to the wafer position detecting systems 20 and 21, the wafer position detecting system 2
By positioning the wafer surface using 0, 21, the lens element 14 and the lens element (1
It is possible to correct the shift of the focal position due to the driving of (5, 16). At this time, the above equation (3) is expressed as the following equation.

ΔF = C _F1 × x ₁ + C _F2 × x ₂ + x ₃ (6) Similarly, the wafer position detection systems 20 and 21 detect the amount of tilt of the wafer surface and control the tilt of the wafer stage to control the projection optical system. It has the function of matching the best image plane of PL. Therefore, similarly to the focus position, if an appropriate offset θ ₃ is given to the tilt amount of the wafer surface, the wafer position detection systems 20, 2
By performing the wafer tilt correction using 1, it is possible to correct the image surface tilt accompanying the driving of the lens element 14. At this time, the above equation (5) can be expressed as follows.

ΔL = C _T2 θ ₁ + θ ₃ (7) Similarly, when the reticle R is translated in the optical axis direction, each of the distortion aberration D and the focus position F changes at a rate of change corresponding to the amount of movement. If the driving amount of the reticle R is x ₄ ,
Each of the amounts of change ΔD and ΔF of the distortion aberration D and the focus position F is expressed by the following equations.

ΔD = D _D4 × x ₄ (8) ΔF = C _F1 × x ₁ + C _F2 × x ₂ + x ₃ + C _F4 × x ₄ (9) In addition, C _D4 and C _F4 are the change amounts. It is a constant representing the rate of change of the reticle R with respect to the driving amount. From the above, (1)
Wherein (2), (4), (7), by setting the driving amount x ₁ ~x ₄ in (9), the amount of change Δ
M, ΔC, ΔT, ΔD, ΔF and ΔL can be arbitrarily corrected. Although the case where six types of image forming characteristics are simultaneously corrected has been described here, among the image forming characteristics of the projection optical system,
If the amount of change in the imaging characteristics due to the thermal deformation of the reticle is negligible, the above correction is not necessary. Further, when the image forming characteristics other than the six types described in the present embodiment change significantly, it is necessary to correct the image forming characteristics. Further, in this embodiment, an example in which the correction is performed by moving the reticle R and the lens element as the image formation characteristic correction mechanism has been shown, but the correction mechanism suitable in this embodiment may be any other method, for example, two A method of sealing the space sandwiched between the lens elements and adjusting the gas pressure in this sealed space may be adopted.

Next, a correction method for the change in the image forming characteristic due to the thermal deformation of the reticle will be briefly described. In FIG. 1, main controller 26 obtains various optical information from irradiation amount monitor 22, photoelectric conversion elements 34 and 35, and image pickup element 33, and controls the shape and size of the opening of variable reticle blind 6 from drive system 7. get information. Then, main controller 26 calculates and calculates the amount of thermal deformation of reticle R and the amount of change in the imaging characteristics of projection optical system PL itself, and at the same time, drive element controller 23 or condensing optical system 21 of the wafer position sensor. Issue a control signal to. Further, the main control system 26 includes various data necessary for calculating the thermal deformation amount of the reticle R (type of light blocking member of reticle, pattern density distribution, etc.).
Is remembered. In addition, a mathematical expression, a table, or the like for calculating the change amount of the imaging state based on the thermal deformation amount is also stored.

A method of calculating the fluctuation amount of the imaging characteristic in this embodiment will be described. The present embodiment corrects a change in the imaging characteristic caused by the thermal deformation of the reticle R. In the present embodiment, the thermal deformation of the reticle R is first calculated when calculating the variation amount of the imaging characteristic. Find the amount. Less than,
The method will be described. Since it can be considered that the thermal deformation of the reticle R occurs in proportion to the temperature distribution of the reticle R, it is sufficient to know the temperature distribution of the reticle R at a certain time in order to calculate the thermal deformation amount. For example, as a method of simulating this temperature distribution with a computer, a method is known in which the reticle R is decomposed into certain finite elements and the temperature change at each point is calculated by a difference method, a finite element method, or the like.

For example, the square exposure area of the reticle R is divided into blocks of about 4 × 4. The number of divisions or the calculation method may be selected in consideration of the finally required accuracy and the calculation speed of the computer. Since the heat absorption of the reticle R varies depending on the density of the reticle pattern, it is necessary to obtain the pattern existence rate of each block. The pattern existence rate is obtained, for example, by the amount of light received by the irradiation amount monitor 22 on the wafer stage 9 in FIG. Further, it is necessary to obtain the heat absorption rate of the light blocking member of the reticle R,
This is common to each block of the reticle R, and is obtained, for example, by obtaining the reflectance of the light shielding member from the amount of light received by the photoelectric conversion element 34 or 35.

When the light source 1 is a pulse light source such as an excimer laser light source and the power varies for each pulse emission,
At the same time, the power of each pulsed light may be measured by the photoelectric conversion element 34. These pieces of information may be directly input to the main controller 26 from the bar code reader 27 or the console 36 instead of being directly measured as described above.
From the above, the amount of heat absorbed by each block of the reticle R is obtained. Next, the amount of heat transfer between each block is calculated. That is, the main controller 26 calculates the process in which heat is transferred from the high temperature portion to the low temperature portion.

In the reticle R, heat escapes not only between the blocks but also in the spaces above and below the reticle holder 18 and the reticle R. The temperature of each block can be obtained by sequentially calculating the amount of heat transfer. Generally, a digital computer adopts a method of obtaining a solution by repeatedly performing calculations. At this time,
In order to obtain information on the heat absorption of the reticle R with respect to time, information from the shutter drive system 3 or the photoelectric conversion element 34 is repeatedly obtained for each calculation. The thermal deformation amount of the reticle R can be obtained from the temperature of each block. This allows the reticle R
We can see how each of the points above moved.

Next, the magnification change Δ by the correction mechanism described above.
The correction amount that minimizes the error when the respective components of M, the trapezoidal distortion ΔT, the distortion aberration ΔD, and the field curvature ΔC are corrected is obtained, and the correction amount is corrected. The correction amount is calculated by, for example, the method of least squares or the method of minimizing the maximum error point. Now, to calculate the above heat conduction,
It is necessary to obtain in advance heat transfer between the blocks of the reticle R, or to obtain a parameter indicating the characteristics of heat that escapes to the space around the reticle holder 18 and the reticle R.
These parameters are numerical values determined by the material of the glass of the reticle R or the flow of ambient air, and are obtained in advance by experimental or simulation calculations. These parameters are stored in memory within main controller 26.

The above description has been made on the case where the reticle R is not equipped with a pellicle as a dustproof film. However, even for reticles having the same pattern and the same material, the amount of heat that escapes to the space above and below the reticle R among the above characteristics differs depending on the presence or absence of a pellicle. That is, even if exposure is performed with illumination light of the same energy, the amount of temperature rise varies depending on the presence or absence of the pellicle, and the amount of change in the imaging characteristics due to thermal deformation of the reticle also differs.

FIG. 4 schematically shows a reticle with a pellicle and a reticle without a pellicle. The influence of the presence or absence of the pellicle will be described with reference to FIG. Usually, the projection exposure apparatus is a system in which the temperature is controlled with high accuracy and clean air is constantly circulated. In particular, in order to prevent foreign matters from adhering to the periphery of the reticle and wafer, air is blown from the lateral direction as shown in FIGS. 4 (a) and 4 (b).
Therefore, in the case of FIG. 4A where there is no pellicle, heat is directly taken from the surface of the reticle R. However, in the case of the reticle R with a pellicle shown in FIG. 4B, heat is only taken from the surfaces of the pellicles 28 and 29. Moreover, since the space between the pellicles 28 and 29 and the glass substrate of the reticle R is filled with air having a good heat insulating property, the efficiency of heat escape is extremely small as compared with the case without the pellicles 28 and 29. .

In other words, when there is no pellicle 28 or 29 on the surface of the glass substrate of the reticle R, heat transfer occurs between the surface of the glass substrate and the air flowing at the temperature set by the apparatus. In the case of the reticle, heat transfer occurs between the reticle and the air that has been warmed and is not flowing. The heat transfer is generally proportional to the temperature difference between the two, and the heat transfer is more efficient if the flow velocity of the other gas is high. Therefore, in the case of the reticle R with the pellicle as shown in FIG. 4B, the efficiency of heat transfer is lower than that of the reticle R without the pellicle as shown in FIG. 4A. Also,
The temperature rise of the reticle R depends on the amount of heat absorbed from the exposure light,
It is determined by the balance with the amount of heat that escapes to the outside. Therefore, in the case of the reticle with the pellicle, the amount of heat that escapes is small, so that the reticle can be balanced at a higher temperature than the reticle without the pellicle. This indicates that the reticle R with a pellicle has a larger amount of thermal deformation.

Experiments have confirmed that the reticle with the pellicle has a thermal deformation amount of about 1.5 to 2 times that of the reticle without the pellicle. The presence or absence of a pellicle is not common to all reticles used in the same projection exposure apparatus, and from the viewpoint of cost and ease of use, for example, a reticle with a rough pattern does not have a pellicle, and a reticle with a fine pattern has a pellicle. The law is adopted. Therefore, it is necessary to inform main controller 26 of the presence or absence of the pellicle by some means and change the parameters for calculating the thermal deformation amount of the reticle. In this embodiment, as shown in FIG. 1, pellicle discriminators 24 and 25 composed of, for example, a non-contact photoelectric sensor or a contact switch are arranged above and below the reticle R,
Information on the presence or absence of a pellicle detected by the pellicle discriminators 24 and 25 is transmitted to the main controller 26.

However, the information on the presence / absence of the pellicle on the reticle R is set by the operator from the console 36 to the main controller 26.
You may enter in. The pellicles 28 and 29 in FIG. 1 are stretched on the upper and lower surfaces of the reticle R.
If the thickness of the glass substrate is sufficient, the pellicle can be attached only to the lower surface (pattern forming surface) of the reticle R. Therefore, the pellicle discriminators 24 and 25 are set to the reticle R.
It is desirable to provide both on the upper and lower surfaces and determine the number of pellicles as well as the presence or absence of pellicles. Further, it may be considered that only the pellicle frames 30 and 31 are adhered to the reticle R and only the pellicles 28 and 29 are not present. Therefore, the pellicle discriminators 24 and 25 determine whether or not the pellicles 28 and 29 themselves are present. Good.

Some projection exposure apparatuses are equipped with a foreign matter inspection apparatus for inspecting the state of adhesion of foreign matter such as dust to the reticle R. Further, the foreign matter adheres to the pellicle mounted on the reticle R. Some can check the condition. In such a foreign matter inspection apparatus, the presence or absence of the pellicle can be discriminated, or the operator inputs the presence or absence of the pellicle in some way. Therefore, the presence or absence of the pellicle is notified from the foreign matter inspection apparatus to the main controller 26. May receive. The difference in the characteristics depending on the presence or absence of the pellicle may be previously obtained by an experiment or the like, and this result may be stored in the main controller 26.

Further, in the pellicle, as shown in FIG. 5, ventilation holes 51 and 53 are formed in parts of the pellicle frames 30 and 31, respectively, and a filter is provided to prevent foreign matter from entering there. In some, members 52 and 54 are provided. The purpose of these ventilation holes 51, 53 is to change the atmospheric pressure around the pellicles 28, 29 so that the pellicle 2 is
This is to prevent 8, 29 from bulging inward or outward.
The size of the ventilation holes 51 and 53 and the filter member 5
It is conceivable that heat may flow in and out of the ventilation holes 51 and 53, though a slight amount, due to resistance or the like when air passes through 2, 54. Therefore, the information of the ventilation holes 51, 53 and the filter members 52, 54 may be input to the main controller 26 as needed. As described above, the thermal deformation of the reticle can be satisfactorily corrected even with respect to the difference in heat transfer characteristics due to the presence or absence of the pellicle.

In the above example, the method of indirectly correcting the information based on the presence / absence of the pellicle is shown, but a method of directly measuring the temperature inside the pellicle is also conceivable. Figure 6 shows the pellicle 2
6 shows a case where the temperature inside 8 and 29 is directly measured. In FIG. 6, temperature sensors 61 and 62 are guided inside the pellicles 28 and 29 through through holes formed in the pellicle frames 30 and 31, respectively. ing. Information on the temperatures near the upper and lower surfaces of the reticle R actually measured by the temperature sensors 61 and 62 is supplied to the main controller 26.

Conversely, if there is no pellicle, the reticle R
Even if the temperatures of the upper and lower surfaces are measured, the temperature is fluctuated due to the mixture of the air temperature-controlled and kept at a constant temperature and the air warmed by the reticle R, so there is no point in measuring the temperature. . On the other hand, it is considered that the inside of the pellicle is a sealed space, and the inside of the pellicle has a substantially uniform temperature due to convection or the like. Therefore, it makes sense to measure the temperature. As described above, the heat conduction between the glass substrate of the reticle R and the air inside the pellicle is proportional to the temperature difference, so the above heat transfer amount can be estimated by measuring the temperature inside the pellicle, and the main controller There is an advantage that the calculation inside 26 can be performed more accurately. Further, if only anisotropic distortion such as magnification and distortion is considered without considering anisotropic deformation (for example, trapezoidal distortion) in the reticle R, the temperature of the air in the pellicle and the wafer A correlation may be established between the amount of change in the image formation characteristics of the image projected onto the image. According to this method, it is not necessary to perform complicated calculation inside the main controller 26.

In the examples so far, the temperature inside the pellicles 28 and 29 has been a problem.
Since 1 is directly bonded to the glass surface of the reticle R, if the adhesive force is strong, the pellicle frames 30, 31
The expansion and contraction of may affect the expansion and contraction of the reticle R itself. Therefore, the main controller 26 also uses the adhesive used for bonding or the bonding method (pressure, temperature, etc. when bonding) as information.
May be input to determine whether or not the expansion and contraction of the pellicle frames 30 and 31 is effective. In addition, when the pellicle frames 30 and 31 are effectively expanded and contracted, the expansion coefficient differs depending on the material, so it is necessary to input the material or expansion coefficient of the pellicle frames 30 and 31. Since the pellicle frames 30 and 31 are usually made of metal, the pellicle frame 3
The coefficient of thermal expansion of 0 and 31 is larger than that of the glass substrate of the reticle R, and it is considered that the expansion amount of the reticle R increases following the pellicle frames 30 and 31. The pellicles 28 and 29 are also usually made of a material having a high transmittance, but the pellicles 28 and 29 themselves absorb the exposure light and function to heat the air layer between the pellicles 28 and 29 and the reticle R. There is also a possibility. So, if necessary,
The material, transmittance, or thickness of the pellicles 28, 29 may be input to the main controller 26 as pellicle information, and the thermal deformation amount of the reticle R may be calculated using this pellicle information.

Naturally, the material, thickness, etc. of the glass substrate of the reticle R also have an effect on thermal expansion, so it is necessary to input information on these glass substrates to the main controller 26 and use these information. Normally, as the glass substrate of the reticle R, quartz glass having a good light transmittance and a small coefficient of thermal expansion is used, but it is also conceivable to use other materials in terms of price and the like. On the contrary, it can be said that inexpensive glass can be used as the glass substrate of the reticle R in the apparatus having the correction function for the change in the image forming characteristic due to the thermal deformation amount of the reticle R as in the present embodiment. If the glass substrate of the reticle R is thick, the heat capacity increases, and the time constant of heat conduction generally increases, so that the thermal expansion amount of the reticle R decreases with respect to the energy of the same illumination light. Therefore, the information on the thickness of the glass substrate of the reticle R is effective information for calculating the thermal deformation amount of the reticle R.

In all of the above-described embodiments, the correction is performed based on the calculation inside the main controller 26 of FIG. 1, but the image is drawn on the reticle R by the image pickup device 33 of the reticle alignment microscope 32, for example. It is also possible to actually observe the position of the alignment mark, measure the thermal deformation amount of the reticle R from the change in the position, and correct it based on this result. Even in this case, since the thermal deformation amount inside the reticle R is unknown, such actual measurement may be combined with the calculation inside the main controller 26. Further, in order to observe the alignment mark of the reticle R, it is necessary to illuminate the alignment mark with the illumination system of the reticle alignment microscope 32 as shown in FIG. 1, and this illumination light may expose the photoresist on the wafer W. There is. Therefore, the thermal deformation amount of the reticle R cannot be actually measured during the exposure operation. Therefore, for example, a method of measuring the thermal deformation amount of the reticle R each time the wafer is exchanged and interpolating by calculation during the period may be considered.

When a projection exposure apparatus that uses a reticle with a pellicle and a projection exposure apparatus that does not use a reticle with a pellicle are used separately, each projection exposure apparatus is fixed to either one. The thermal deformation amount of the reticle may be calculated using the parameters. Also,
If the control error is acceptable even with the thermal deformation amount of the reticle calculated using the parameter between the two,
The amount of thermal deformation of the reticle may be calculated by using an intermediate parameter in each type of projection exposure apparatus.

Further, in the above-mentioned embodiment, the pellicle as the dustproof film is used to prevent the foreign matter from adhering to the reticle R. However, when a cover glass is used instead of the pellicle, the cover glass is used. Information about the presence / absence of information is input to the main controller 26, and the main controller 26 may calculate the thermal deformation amount of the reticle R from the information. As described above, the present invention is not limited to the above-described embodiments, and various configurations can be taken without departing from the gist of the present invention.

[0058]

According to the present invention, mask shape data (information such as the presence or absence of a dustproof film) is input, and the amount of thermal deformation of the mask, and thus the amount of change in the image formation state, is calculated based on this shape data. Since the image forming state is corrected so as to cancel out the change amount of the image forming state, there is an advantage that the mask pattern can be always projected and exposed on the photosensitive substrate in the predetermined image forming state regardless of the presence or absence of the pellicle. is there.

If the shape data is data indicating the presence or absence of a protective member for preventing foreign matter from adhering to the pattern forming surface of the mask and the thickness of the mask, the amount of thermal deformation of the mask. Can be calculated accurately. Further, a temperature measuring means for measuring the temperature inside the protective member of the mask is provided, and the calculating means is based on the temperature information obtained by the temperature measuring means and the shape data inputted from the data input means. , When calculating the change amount of a predetermined image formation state caused according to the thermal deformation amount of the mask,
The thermal deformation amount of the mask can be calculated more accurately.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an entire embodiment of a projection exposure apparatus according to the present invention.

FIG. 2 is a perspective view showing a reticle with a pellicle shown in FIG.

FIG. 3 is a diagram showing an example of correction of distortion of a projected image by the image formation characteristic correction mechanism of the embodiment.

FIG. 4 is a diagram schematically showing a state where heat accumulated in a reticle due to absorption of illumination light is released to air.

FIG. 5 is a cross-sectional view showing a structure in which a vent hole is formed in a pellicle frame of a reticle with a pellicle.

FIG. 6 is a cross-sectional view showing a configuration for measuring the temperature of air inside a pellicle of a reticle with a pellicle.

[Explanation of symbols]

 1 Light Source R Reticle PL Projection Optical System W Wafer 12, 13, 19 Driving Element 20 Wafer Position Sensor Irradiation Optical System 21 Wafer Position Sensor Receiving Optical System 22 Irradiation Level Monitor 23 Driving Element Controller 24, 25 Pellicle Discriminator 26 Main Control device 27 Bar code reader 28,29 Pellicle 30,31 Pellicle frame 36 Console

Claims (3)

[Claims] 1. A projection exposure apparatus comprising: an illumination optical system that illuminates a pattern on a mask with illumination light; and a projection optical system that exposes an image of the pattern on the mask onto a photosensitive substrate in a predetermined image formation state. Data input means for inputting shape data representing the shape of the mask, and based on the shape data input from the data input means, a change amount of the predetermined image formation state caused according to a thermal deformation amount of the mask. A projection exposure apparatus comprising: calculation means for calculating; and image formation state correction means for correcting the image formation state of the projection optical system so as to cancel the amount of change calculated by the calculation means. 2. The shape data is data indicating the presence or absence of a protective member for preventing adhesion of foreign matter to the pattern formation surface of the mask, and the thickness of the mask. Projection exposure equipment. 3. When the mask is equipped with a protective member for preventing foreign matter from adhering to the pattern formation surface, temperature measuring means for measuring the temperature inside the protective member is provided, and the calculation is performed. The means is based on the temperature information obtained by the temperature measuring means and the shape data input from the data input means, and the change amount of the predetermined image formation state caused according to the thermal deformation amount of the mask. The projection exposure apparatus according to claim 1 or 2, wherein