JPH11162830A - Aligning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aligning method, which corrects a measuring error in a sensor for measuring the light amount and measures with high precision radiated amount and an accumulated aligning amount, even when the radiated amount is changed over a wide range without providing special cooling mechanisms. SOLUTION: When an illuminous light IL is radiated and a pattern of a reticle R is aligned to a wafer W, a thermal drift which is overlapped on an output signal (irradiated energy) Ek measured by a luminous intensity variations sensor 49, which receives the illuminuous light IL and photoelectrically converts is acquired, based on the measured output signal Ek from equation yk+1 =exp(-Δt/T)yk +Czi (1-exp(-Δt/T))Ek (where Δt is a sampling period, yk is thermal drift, T is a time constant, Ek is radiated energy and Czi is a constant). A true radiated energy Ekz is acquired, based on the output signal Ek and the thermal drift yk+1 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method used in a photolithography process for manufacturing a semiconductor device, a liquid crystal display device, a thin film magnetic head, or the like.

[0002]

2. Description of the Related Art In a photolithography process in a manufacturing process of a semiconductor device or a liquid crystal display device, a circuit pattern formed on a reticle or a mask (hereinafter, referred to as a reticle) is formed on a semiconductor wafer or glass plate (hereinafter, referred to as a reticle) via a projection optical system. , A wafer) is used. There are various types of projection exposure apparatuses. For example, in the case of manufacturing a semiconductor device, a wafer is step-and-stepped through a projection optical system having an image field capable of projecting the entire reticle circuit pattern at one time. There are a projection exposure apparatus that performs exposure by a repeat method, and a projection exposure apparatus that employs a so-called step-and-scan method that scans a wafer one-dimensionally at a speed synchronized with that while scanning a reticle one-dimensionally.

By the way, these projection exposure apparatuses are required to have high exposure accuracy, and therefore, are provided with an illuminance control mechanism for optimizing an exposure amount (exposure energy) to each shot area of a wafer. . For example, FIG. 5 shows a step-and-repeat type projection exposure apparatus provided with a conventional illuminance control mechanism. In FIG. 5, illumination light from a mercury lamp 101 is collected after being converged by an elliptical mirror 102. The light reaches the shutter 104 via a light-collecting optical system 103a and a light-collecting filter system 103 including an optical filter 103b for selecting light in a desired wavelength band (for example, i-line). The shutter 104 is opened and closed by a shutter control mechanism 105 based on a command from a timer control system 106.
When the shutter 104 is in the open state, the illuminating light enters the fly-eye lens 108 as a substantially parallel light beam via the input lens 107.

A large number of secondary light source images are formed on the exit surface of the fly-eye lens 108, and these are used to form a reticle 119.
The illumination intensity distribution of the illumination light for illuminating is flattened. The illumination light having passed through the fly-eye lens 108 enters a reflection mirror 109 having a reflectance of about 98%. The illumination light reflected by the reflection mirror 109 illuminates the illumination area on the reticle 119 with a uniform illuminance distribution via the first relay lens 113, the second relay lens 116, the reflection mirror 117, and the condenser lens 118. By this illumination light, the pattern on the reticle 119 is reduced to, for example, 1/5 through the projection optical system 120 and projected and exposed on each shot area of the wafer 121.

At the time of the exposure operation by the conventional projection exposure apparatus, the light transmitted through the reflection mirror 109 is condensed by a condenser lens 110.
Is incident on an integrator sensor 111, which is an optical sensor that performs photoelectric conversion, and the output signal is transmitted to an illuminance calculation system 112.
Supplied to The integrator sensor 111 is, for example, at a position substantially conjugate with the pattern forming surface of the reticle 119. The conversion coefficient between the exposure energy per unit time on the wafer 121 and the illuminance on the integrator sensor 111 is stored in the illuminance calculation system 112 in advance. By multiplying the output signal of the integrator sensor 111 by the conversion coefficient in the illuminance calculation system 112, the exposure energy per unit time on the wafer 121 is obtained. The obtained exposure energy per unit time is supplied to the main control system 125. The main control system 125 sets a timer for an exposure time obtained by dividing an appropriate exposure amount on the wafer 121 by the exposure energy per unit time. Input to the control system 106. In response, the timer control system 106 opens the shutter 104 for the exposure time, so that the integrated exposure amount on the wafer 121 is controlled to an appropriate exposure amount.

[0006]

In recent years, the wafer size has been increased in order to improve the throughput of the apparatus, and so-called one-shot multiple-chip exposure in which a plurality of chips are collectively transferred within a shot area to be collectively exposed. Are being performed, and accordingly, the shot area is being enlarged, that is, the projection area is being enlarged. In order to cope with the enlargement of the projection area, it is necessary to avoid long-time irradiation of illumination light from the viewpoint of throughput. Therefore, in order to obtain a predetermined integrated exposure amount, the amount of illumination light of the light source is increased. Will be. For this reason, the integrator sensor at the time of measuring the amount of light is irradiated with a larger amount of light than before, which may cause a problem that the temperature of the integrator sensor increases and the sensor sensitivity changes.

Further, recently, in order to improve the resolution and the depth of focus of a periodic pattern having a small pitch, for example, a plurality of types of illumination system aperture stops (not shown) are provided on the light exit side of the fly-eye lens 108. It is provided so that it can be selected. As the illumination system aperture stop, for example, there are a modified light source method having a plurality of apertures decentered with respect to the optical axis, an annular illumination method having an annular aperture shape, and the like. In order to maintain the S / N ratio of the output of the integrator sensor at a predetermined value or more with respect to the change in the irradiation light amount due to the change of the illumination condition, a light amount of a certain light amount or more is given to the integrator sensor. A problem arises in that the temperature change of the integrator sensor occurs at the time of the light quantity measurement, and the sensor sensitivity changes.

On the other hand, in a step-and-scan type projection exposure apparatus, since the exposure is performed by scanning a slit-like exposure field shorter than the length of the shot area of the wafer, the integrated exposure amount on the wafer surface is increased. In order to maintain a constant value, the absolute irradiation amount, which is the amount of exposure that is applied per unit time to the entire exposure field per unit time, is increased by the smaller illumination area compared to the batch exposure method, and the integrated exposure amount is adjusted according to the resist sensitivity. Since it is necessary to make the variable in a wide range, it is necessary to make the variable range of the irradiation amount large.

However, in order to maintain the S / N ratio of the output of the integrator sensor at a predetermined value or more both when the irradiation light quantity is large and when the irradiation light quantity is small, it is necessary to use an integrator. Since a certain amount of light is given to the sensor, there is a problem that the temperature of the integrator sensor changes at the time of measuring the amount of light and the sensor sensitivity changes in the same manner as described above. In addition, since the irradiation amount on the wafer stage is larger than that of the batch exposure method, the illumination light of a wide range of irradiation is used to measure the illuminance unevenness sensor which is a photoelectric sensor on the wafer stage and the amount of reflected light from the wafer. Irradiation to the irradiation amount monitor, which is a photoelectric sensor, causes a temperature change that cannot be ignored on these photoelectric sensors, and there is also a problem that the sensor sensitivity changes.

In recent years, as disclosed in Japanese Patent Application Laid-Open No. 9-22120, there has been proposed an integrator sensor capable of suppressing a change in temperature and maintaining the sensor sensitivity within a predetermined range even when a large amount of light is applied. FIG. 6 is a plan view of the improved integrator sensor 33. FIG. 6, heat exchangers (Peltier elements) 71a and 71b are fixed to the left and right side surfaces of the integrator sensor 33 main body. A member having high thermal conductivity is used for a portion outside the circular irradiation field 76 at the center of the light receiving surface 77 of the integrator sensor 33, and the heat absorbing sides (low temperature side) of the heat exchangers 71a and 71b are connected to the member. Directly fixed. The heat generated by irradiating the irradiation field 76 with the illumination light is absorbed by the heat exchangers 71a and 71b from the left and right side walls of the member having a high thermal conductivity on the light receiving surface 77. Heat exchangers 71a, 7
A cooling pipe 73 is tightly fixed to the bottom surface of the heat radiation side (high temperature side) opposite to the heat absorption side of the heat exchanger 1b.
The heat on the heat radiation side of a and 71b is taken away by the cooling water circulating in the cooling pipe 73 leading to an external temperature control device (not shown).

A temperature sensor 75 is installed near the outer periphery of the irradiation field 76, and the temperature around the irradiation field 76 is constantly measured. The measured value of the temperature sensor 75 is supplied to a temperature control system 79,
9 controls the power supplied to the heat exchangers 71a and 71b based on the measured values. The measurement value of the temperature sensor 75 is also supplied to the main control system 125, and the main control system 125 corrects the measurement value of the light amount of the integrator sensor 33 based on the temperature measurement value.

As described above, by providing the temperature sensor 75 for measuring the temperature of the light receiving surface 77 of the integrator sensor 33, the temperature of the integrator sensor 33 is intended to be used for correcting the measured value of the irradiation amount.

[0013] However, in order to cool the light receiving surface of the optical sensor with the heat exchanger composed of such a Peltier element,
It is necessary to provide a special cooling mechanism as described above,
The high cost of the equipment cannot be avoided. In addition, for example, in order to attach the cooling mechanism to an illuminance unevenness sensor provided on a movable portion such as an XY stage or an irradiation amount monitor, there arises a problem in space and a problem in that wiring and piping are difficult. In addition, since the thermal effect of the XY stage itself directly leads to the deterioration of the stage performance, it is not preferable to dispose another heat exchanger inside the XY stage.

According to the present invention, even if the irradiation amount is changed over a wide range without providing a special cooling mechanism, the measurement error of the sensor for measuring the light amount is corrected, and the measurement of the irradiation amount or the integrated exposure amount is improved. An object of the present invention is to provide an exposure method performed with high accuracy.

[0015]

The object of the present invention will be described with reference to FIGS. 1 to 4 showing an embodiment of the present invention. The object is to irradiate illumination light (IL) to change the pattern of a reticle (R). In an exposure method for exposing a substrate (W), an optical sensor (33, 4) for receiving illumination light (IL) and performing photoelectric conversion.
9, 53, 55) is calculated by calculation based on the measured output signal, and the amount related to the irradiation energy of the illumination light (IL) is calculated based on the output signal and the heat drift amount. It is attained by an exposure method characterized by what is sought. In the above exposure method, the amount of thermal drift is:

Y _{k + 1} = exp (−Δt / T) y _k + C _zi (1-exp (−Δt / T)) E
_k

(Where Δt is a sampling period, y _k is a thermal drift amount, T is a time constant, E _k is an irradiation energy, and C _zi is a constant).

In the above exposure method, the illumination light (I
The quantity relating to the illumination energy in L) is the illuminance unevenness. The drift amount is calculated based on the sampling cycle of the optical sensor.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An exposure method according to one embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the present invention is applied to a step-and-scan type projection exposure apparatus. FIG. 1 shows a projection exposure apparatus according to the present embodiment. In FIG. 1, illumination light from a mercury lamp 1 is collected by an elliptical mirror 2. A shutter 4 that is opened and closed by a shutter control mechanism 5 is disposed in the vicinity of the converging point. When the shutter 4 is in an open state, the illumination light is converted into a substantially parallel light beam via the mirror 3 and the input lens 6. The field stop 7 is reached. Immediately after the field stop 7, a dimming plate 23 is disposed so as to be able to be taken in and out so that the amount of illumination light passing through the field stop 7 can be changed stepwise or continuously within a predetermined range by the dimming plate 23. Has become.

The dimming plate 23 is, for example, one in which a plurality of reflection type half mirrors are arranged so as to be switchable, and the inclination of each half mirror with respect to the optical axis is set so that the transmittance as a whole becomes a predetermined transmittance. Have been. Then, the dimming plate driving mechanism 24 including the driving motor drives the dimming plate 2
By moving step 3 in steps, the amount of illumination light is adjusted. In the present embodiment, it is the exposure control system 20 that controls the exposure for the wafer W, and the exposure control system 20 controls the operation of the dimming plate driving mechanism 24,
It also controls the operation of the shutter control mechanism 5. Further, the exposure amount control system 20 is connected to a power supply system 22 for the mercury lamp 1,
The current supplied to the mercury lamp 1 is controlled.

After the aperture of the field stop 7 is properly passed, the light reducing plate 2
The illumination light whose light amount is adjusted by 3 enters the first fly-eye lens 9 of the two-stage fly-eye lens group via the first relay lens 8. Illumination light from a plurality of light source images by the first fly-eye lens 9 is guided to the second fly-eye lens 14. In the present embodiment, the light amount aperture 10 is disposed near the exit surface of the first fly-eye lens 9, that is, near the light source image forming surface, and the aperture of the light amount aperture 10 is arbitrarily large by the light amount aperture driving mechanism 11. It can be adjusted. The operation of the light amount aperture driving mechanism 11 is also controlled by the exposure amount control system 20. In the present embodiment, by adjusting the size of the aperture of the light amount aperture 10, the first
The amount of illumination light traveling from the fly-eye lens 9 to the second fly-eye lens 14 can be continuously adjusted.

An illumination system aperture stop plate 16 in which a plurality of types of illumination system aperture stops are disposed near the exit surface of the second fly-eye lens 14 is provided. The main control system 19 is controlled by an illumination system diaphragm drive mechanism 17 including a drive motor.
The rotation angle of the illumination system aperture stop plate 16 is controlled. After being emitted from the second fly-eye lens 14, the illumination system aperture stop plate 1
Illumination light IL that has passed through the aperture stop selected from 6 is
The light enters the beam splitter 31 having a transmittance of about 98%. The illumination light transmitted through the beam splitter 31 reaches the blind 37 (field stop) via the first relay lens 34. The arrangement surface of the blind 37 is near the Fourier transform surface of the exit surface of the second fly-eye lens 14.
That is, the arrangement surface of the blind 37 is substantially conjugate with the pattern formation surface of the reticle R described later.

The blind 37 is, for example, a mechanical field stop that surrounds a rectangular opening with four knife edges, and the shape of the slit-shaped illumination area on the reticle R is defined by the rectangular opening. That is, the blind 37
The illumination light IL limited by the second relay lens 3
8. Illuminate the slit-shaped illumination distribution area 41 on the reticle R with a uniform illuminance distribution via the condenser lens 39 and the mirror 40.

Then, the image of the pattern in the illumination area 41 on the reticle R is converted into a projection magnification β via the projection optical system PL.
(Β is, for example, １ ／ or ５) and projected onto the slit-shaped exposure field 47 on the wafer W. Here, the Z axis is taken in parallel with the optical axis of the projection optical system PL, and the reticle R and the wafer W during scanning exposure are in a plane perpendicular to the Z axis.
The X axis is taken in parallel with the scanning direction, and the Y axis is taken in a direction perpendicular to the X axis (non-scanning direction) in a plane perpendicular to the Z axis. In the present embodiment, the reticle R is held on a reticle base 43 via a scanning stage 42 slidable in the X direction,
The wafer W is held on a wafer stage 48 that scans the wafer W in the X direction and positions the wafer W in the Y direction. The wafer stage 48 also incorporates a Z stage for positioning the wafer W in the Z direction.

Scanning stage 42 and wafer stage 4
A stage driving mechanism is constituted by 8, and the operation of the stage driving mechanism is controlled by a stage control system 46. During scanning exposure, the stage control system 46 controls the reticle R via the wafer stage 48 in synchronization with scanning the reticle R at a predetermined speed VR in the + X direction (or -X direction) with respect to the illumination area 41 via the scanning stage 42. A predetermined shot area on the wafer W is scanned with respect to the exposure field 47 in the −X direction (or + X direction) at a speed VW (= β · VR). Thus, the pattern of the reticle R is successively transferred and exposed on the shot area.

In the vicinity of the wafer W on the wafer stage 48, an uneven illuminance sensor 49 including a photoelectric detector having a light receiving surface at the same height as the exposure surface of the wafer W is provided.
The uneven illuminance sensor 49 receives a part of the illuminating light from a pinhole-shaped transmitting portion provided on the light receiving surface and detects a variation in illuminance in an exposure field. After driving the pin 48 of the uneven illuminance sensor 49 to the center of the exposure field 47, the illuminance is measured at a plurality of locations in the exposure field 47 while slightly moving the wafer stage 48, and the illuminance at the plurality of locations is measured. Measure the variation in illuminance.

Further, an irradiation amount monitor 55 including a photoelectric detector for measuring the irradiation amount of the exposure field 47 is provided in parallel with the uneven illuminance sensor 49. Irradiation dose monitor 55
Has a light receiving surface large enough to cover the entire surface of the exposure field 47 arranged at the same height as the exposure surface of the wafer W, similarly to the uneven illuminance sensor 49.
8 is driven to cover the entire exposure field 47 with its light receiving surface, and the amount of light incident from the light receiving surface is measured.

Illumination unevenness sensor 49 and irradiation amount monitor 5
The detection signal output from 5 is supplied to a main control system 19, and the main control system 19 controls the dimming plate 23 and the light amount aperture 10 via the exposure amount control system 20 based on the detection signals.

Beam splitter 3 having a transmittance of about 98%
The light reflected by 1 is condensed on a light receiving surface of an integrator sensor 33 composed of a photoelectric detector via a condenser lens 32. The light receiving surface of the integrator sensor 33 is, for example, substantially conjugate with the pattern forming surface of the reticle R and the exposure surface of the wafer W, and the detection signal (photoelectric conversion signal) of the integrator sensor 33 is supplied to the exposure control system 20. I have. The detection signal is also supplied to the power supply system 22 for the mercury lamp 1 and the main control system 19 via the exposure amount control system 20.

A memory 21 is connected to the exposure amount control system 20. In the memory 21, a conversion coefficient and the like for obtaining an irradiation amount (exposure amount per unit time) on the wafer W from an output signal of the integrator sensor 33 are stored. Is stored. However, in the present embodiment, the output signal of the integrator sensor 33 is calibrated using, for example, a predetermined reference illuminometer,
A correction coefficient for correcting the output signal of the integrator sensor 33 based on the calibration result is also stored in the memory 21.

The light receiving surface of the integrator sensor 33 is arranged at a position substantially conjugate with the pattern surface of the reticle R, so that even when the illumination system aperture stop plate 16 is rotated to change the shape of the illumination system aperture stop. In this way, no error occurs in the detection signal of the integrator sensor 33. However, the light receiving surface of the integrator sensor 33 is arranged on an observation surface that is substantially conjugate with the Fourier transform surface (pupil surface) of the reticle pattern in the projection optical system PL, and can receive all light beams passing through this observation surface. It does not matter.

In this embodiment, the transmittance is 98%.
On the side opposite to the integrator sensor 33 with respect to the beam splitter 31, a condensing lens 52 and a wafer reflectance monitor 53 including a photoelectric detector are provided. Is almost conjugate to the surface of In this case, of the illumination light transmitted through the reticle R and irradiated onto the wafer W via the projection optical system PL, the reflected light on the wafer W is reflected on the wafer via the projection optical thread PL, the reticle R and the like. The light is received by the rate monitor 53, and the detection signal (photoelectric conversion signal) is supplied to the main control system 19. In the main control system 19, the reticle R
The projection optical system PL is based on the light energy per unit time of the illumination light IL irradiated to the side and the light energy per unit time of the reflected light on the wafer W calculated from the detection signal of the wafer reflectance monitor 53. Light energy per unit time of the illumination light passing through is obtained. Further, the main control system 19 predicts the thermal expansion amount of the projection optical system PL based on the thermal energy obtained by multiplying the light energy thus obtained by the exposure time, and performs the projection based on the predicted thermal expansion amount. The amount of change in imaging characteristics such as distortion of the optical system PL is obtained. Then, the main control system 19 corrects the imaging characteristic of the projection optical system PL to the original state via an imaging characteristic correction mechanism (not shown) connected to the projection optical system PL.

FIG. 2 is a system diagram showing a main portion of the exposure amount control system described above, and as shown in FIG. 2, as shown in FIG.
The light amount L is adjusted by the illumination system aperture stop plate 16, the light amount stop 10, and the light reduction plate 23, and is transmitted to the reticle R almost (98%) through the beam splitter 31. Then, the illumination light IL transmitted through the reticle R is irradiated onto the wafer W. In this exposure amount control system, the exposure amount of the illumination light IL is measured by photoelectric sensors (photoelectric detectors) provided at four locations. The first photoelectric sensor is an integrator sensor 33 that receives light reflected by the beam splitter 31 and measures light energy per unit time. This sensor detects a part of the amount of illumination light IL from the mercury lamp 1. Detect directly. The second photoelectric sensor is a wafer reflectance monitor 53 that receives light reflected from the wafer W and reflected by the beam splitter 31 and measures light energy per unit time, and passes through the projection optical system PL. The main purpose is to detect the amount of light and correct the imaging characteristics of the projection optical system PL. The third and fourth photoelectric sensors are an uneven illuminance sensor 49 and an irradiation amount monitor 55 having a light receiving surface on the same plane as the wafer W, and detect the illuminance unevenness in the exposure field and the total irradiation amount in the exposure field, respectively. I do.

The measured value of the integrator sensor 33 is supplied to the exposure control system 20. The measured value of the integrator sensor 33 is also supplied to the main control system 19 via the exposure control system 20, and the main control system 19 corrects the measured value and supplies it to the exposure control system 20. The exposure amount control system 20 controls the intensity of the mercury lamp 1 via a power supply system 22 based on the correction value, and also controls the light amount aperture 10 and the light reduction plate 23 via the respective light amount aperture drive mechanisms 11 and the light reduction plate drive mechanisms 24. Control. The measured values of the wafer reflectance monitor 53, the illuminance unevenness sensor 49, and the irradiation amount monitor 55 are supplied to the main control system 19, and the main control system 19 controls the illumination system diaphragm drive mechanism 17 based on the measured values. The degree of opening of the illumination system aperture stop plate 16 is adjusted via this.

In the exposure amount control system having the above configuration, it is extremely important to detect the exposure amount with high accuracy by the above three photoelectric sensors. Since the sensor is directly exposed to light, a measurement error may occur due to a temperature change due to a temperature rise of the sensor itself. Therefore, in the present embodiment, the drift of the sensor sensitivity caused by the temperature change of the sensor body due to the heat applied to the photoelectric sensor is corrected by the method described below.

Hereinafter, a method for correcting drift in sensor sensitivity according to the present embodiment will be described with reference to the uneven illuminance sensor 49 shown in FIGS. 1 and 2 as an example. As described above, the temperature of the light receiving surface of the uneven illuminance sensor 49 changes in accordance with the accumulated amount of irradiation energy applied to the light receiving surface. When the temperature drift of the light receiving surface occurs, the sensitivity characteristic of the uneven illuminance sensor 49 changes accordingly. In the present embodiment, the relationship between the amount of irradiation energy previously applied to the light receiving surface of the illuminance sensor 49 and the amount of thermal drift of the light receiving surface of the uneven illuminance sensor 49,
The relationship between the illuminance unevenness sensor 49 and the sensitivity characteristic of the uneven illuminance sensor 49 with respect to the thermal drift is determined in advance. The amount of illumination light incident on the uneven illuminance sensor 49 is corrected based on these two relations obtained in advance.

FIG. 3 is a plan view schematically showing the light receiving surface of the uneven illuminance sensor 49 of the projection exposure apparatus according to the present embodiment. The illuminance sensor 49 according to the present embodiment is characterized in that its sensitivity can be corrected without providing any special hardware such as a cooling mechanism for controlling the temperature of the light receiving surface of the illuminance sensor 49 which fluctuates due to irradiation energy. doing.

First, the measurement by the illuminance unevenness sensor 49 will be briefly described. After the light receiving surface 77 of the illuminance unevenness sensor 49 substantially matches the image forming surface of the projection optical system PL, a part of the exposure light on the image forming surface Is received by the light receiving area 76. This light receiving operation is performed for a plurality of measurement points set in advance in the image plane (in the shot area), and the illuminance distribution (illuminance unevenness) in the image plane is measured. In this way, when measuring the illuminance unevenness, the illuminance unevenness sensor 49 is constantly exposed to the exposure light, and the illuminance unevenness sensor 49 receives the exposure light from the light receiving surface 77 to reduce a part of the irradiation energy. Absorbed as heat energy, the temperature rises. As the temperature rises due to this heat, a drift occurs in the sensor sensitivity.

This will be described with reference to FIG. FIG. 4 shows that the irradiation unevenness sensor 49 absorbs / irradiates the exposure light with and without irradiation.
It indicates the change in stored thermal energy,
The measurement is a result discretely performed at a predetermined sampling time. The horizontal axis shows the sampling time (sec), and the vertical axis shows the irradiation heat energy amount (mJ) as an integral value of the heat energy. The example shown in FIG. 4 shows a change in thermal energy when exposure light irradiation, light shielding, and exposure light irradiation are sequentially performed during the entire sampling period.

In FIG. 4, each sampling time point S1, S2,
.., The circle mark shown for each point indicates an uneven illuminance sensor 49 at each time point.
Shows the total amount of heat energy stored in the memory. As is clear from the figure, at the time of irradiation (for example, S1 to S3 or S6 to S9) during which the exposure light is irradiated, the total amount of heat energy applied to the uneven illuminance sensor 49 increases, and In S3 to S5), on the contrary, the heat energy amount decreases. When this is examined in more detail, in the state where the exposure light is irradiated, the sum of the heat energies accumulated in the illuminance unevenness sensor 49 at each sampling time is different from the sum of the heat energies at the previous sampling by the following. The difference between the heat energy that increases due to the irradiation energy of the exposure light irradiated before sampling and the heat energy that decreases due to radiation or the like before the next sampling is added. In the figure, the area between ○ and ● at each sampling point indicates an increase in heat energy at the sampling interval, and the heat energy due to radiation is from the mark at the previous sampling point to the mark at the next sampling point. Shows a decrease. After all, the total amount of heat energy applied to the uneven illuminance sensor 49 is represented by a circle in FIG.
It will change along the curve connecting the marks.

Accordingly, the change in heat energy shown in FIG.
That is, the sensitivity of the uneven illuminance sensor 49 changes in accordance with the amount of thermal drift. Therefore, in the present embodiment, a model equation of the following first-order lag system is created based on the amount of thermal drift as shown in FIG.

Y _{k + 1} = exp (−Δt / T) y _k + C _zi (1−exp (−Δt / T)) E _k Equation (1) (where Δt is a sampling period and y _k is The amount of thermal drift, T is a time constant, E _k is irradiation energy, and C _zi is a constant.)

The left side of the equation (1) is the amount of heat energy (the first term on the right side) already reduced by heat radiation at the current (K-th) sampling time and the exposure measured at the current (K-th) sampling time. As the sum of the amount of heat energy (the second term on the right side) increased by the light irradiation energy E _k ,
(+1) thermal drift amount. From this equation (1), the thermal drift amount y _{k + 1} at the next sampling is estimated from the irradiation energy E _k actually measured by the irradiation unevenness sensor 49 including the error due to the change in the measurement sensitivity due to the thermal drift. Can be. This estimated thermal drift amount y
_The true irradiation energy E _kX corrected for the error due to the thermal drift using _{k + 1} is

E _kX = E _k −α · y _{k + 1} Equation (2) (where α is a predetermined constant)

Can be obtained as follows. As described above, the sensitivity of the illuminance unevenness sensor 49 can be corrected by software processing without providing a special cooling mechanism. Therefore, the correction method according to the present embodiment corrects a change in sensitivity due to a change in the temperature of the light receiving surface of the uneven illuminance sensor 49 for measuring uneven illuminance, which is extremely important in controlling the amount of exposure.
Uniform exposure can be performed on the exposed region.

In the above description, the illuminance non-uniformity sensor 49 of the exposure apparatus has been described as an example. Is also effective. Also, compared to the case where the sensitivity is adjusted by cooling the photoelectric sensor itself using a special cooling mechanism, there is no need to provide extra wiring and piping for the XY stage, and the XY stage is included. Since there is no emission of heat energy from the cooling mechanism that disturbs the atmosphere, the accuracy of the XY stage can be maintained.

Further, the correction method according to the present embodiment
Of course, the present invention can be applied to the integrator 33 and the reflectance sensor 53 arranged in the illumination system, and this is effective in increasing the measurement accuracy of these photoelectric sensors.

In the above embodiment, a continuous light (mercury lamp) is used as an exposure light source. However, even when a pulse light source such as an excimer laser light source is used as an exposure light source, the correction method of this embodiment is used. Can be used.

The present invention is not limited to the above embodiment, but can be variously modified. For example, in the above-described embodiment, the present invention is applied to the exposure measurement sensor of the step-and-scan projection exposure apparatus. However, the present invention is not limited to this. The present invention can of course be applied to a repeat type projection exposure apparatus.

[0050]

As described above, according to the present invention, the measured value of the photoelectric sensor can be corrected even when the light amount largely changes and the temperature of the light receiving surface changes widely, so that the light amount to the photoelectric sensor is limited. No need to do. In addition, a photoelectric sensor is provided in the illumination optical system to partially measure the amount of light flux separated from the illumination light. The photoelectric sensor is disposed on the same surface as the photosensitive substrate and measures the amount of illumination light applied to the photosensitive substrate. In the case of at least one of a photoelectric sensor group consisting of a photoelectric sensor for partially measuring, and a photoelectric sensor arranged on the same surface as the photosensitive substrate and measuring the total amount of illumination light applied to the photosensitive substrate, The irradiation amount during the actual exposure, the illuminance unevenness during the actual exposure, and the actual irradiation amount during the non-exposure are measured with high accuracy.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram showing an exposure control system in the scanning projection exposure apparatus according to one embodiment of the present invention.

FIG. 3 is a plan view schematically showing an uneven illuminance sensor in the scanning projection exposure apparatus according to one embodiment of the present invention.

FIG. 4 is a diagram showing heat energy accumulated in an uneven illuminance sensor due to irradiation of exposure light.

FIG. 5 is a diagram showing a schematic configuration of a conventional projection exposure apparatus.

FIG. 6 is a diagram illustrating cooler light in a conventional integrator sensor.

[Explanation of symbols]

 R Reticle PL Projection optical system W Wafer 1 Mercury lamp 4 Shutter 9 First fly-eye lens 10 Light amount aperture 12A, 12B Second relay lens 14 Second fly-eye lens 16 Illumination system aperture stop plate 19 Main control system 20 Exposure amount control system Reference Signs List 22 power supply system 23 dimming plate 33 integrator sensor 37 fixed blind 42 reticle stage 47 exposure field 48 wafer stage 49 illuminance unevenness sensor 53 wafer reflectance monitor 55 irradiation amount monitor 71a, 71b, 72 heat exchanger 73 cooling pipe 74 heat sink 75 temperature Sensor 77 Light receiving surface 79 Temperature control system

Claims (4)

[Claims] An exposure method for irradiating illumination light onto a substrate to expose a pattern of a reticle to a substrate, the method comprising: measuring an amount of thermal drift superimposed on an output signal of an optical sensor that receives the illumination light and performs photoelectric conversion. An exposure method comprising: calculating an amount based on a signal; calculating an amount related to irradiation energy of the illumination light based on the output signal and the thermal drift amount. 2. The exposure method according to claim 1, wherein the thermal drift amount is y _{k + 1} = exp (−Δt / T) y _k + C _zi (1-exp (−Δt / T)) E _k (However, Δt is the sampling period, y _k is the amount of thermal drift, T
Is a time constant, E _k is irradiation energy, and C _zi is a constant. ). 3. The exposure method according to claim 1, wherein the quantity related to the illumination energy of the illumination light is uneven illuminance. 4. The exposure method according to claim 1, wherein the drift amount is calculated based on a sampling cycle of the optical sensor.