JPH02106917A - Aligner - Google Patents

Abstract

PURPOSE:To optimize exposing behavior conditions in response to transmittance by calculating energy amount stored in a projection optical system on the basis of the transmittance of a mask, the illuminance of an irradiated light or the exposing condition, and so regulating the illuminance of the radiated light as to be allowable storage energy amount or less. CONSTITUTION:A main control system 20 outputs a drive command corresponding to an optimum attenuation amount to a drive system 23 of an attenuation filter 6 on the basis of a signal from an illuminance sensor 21 or a signal from a bar code reader 22. It also outputs a command for supplying suitable power corresponding to an exposure sequence to a power source 24 for driving a mercury lamp 1. The power source 24 confirms supplied power on the basis of a signal from a photoelectric sensor 25 for sequentially detecting the illuminance of the light radiated to a reticle R. The signal from the sensor 25 is also input to a shutter control system when the opening time of a shutter 4 is automatically controlled in an optical amount integration mode, information such as the opening timing of the shutter 4 is communicated, and the shutter 4i can be controlled in response to a set value from the system 20 in a timer mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exposure apparatus used in the manufacture of semiconductor devices, etc.
The invention relates to an exposure apparatus having a laser oscillator, etc.).

(Prior Art) Conventionally, this type of exposure apparatus uses a step-and-repeat projection method in which an image of a pattern area formed on a mask or reticle is projected onto a photosensitive substrate, ie, a photosensitive substrate, through a projection lens system. A mold exposure device, a so-called stepper, is known.

Currently, the steppers used at IC1VLSI manufacturing sites have a wavelength of 436 nm (g-line) or 365 na+ (
The light source for exposure is a mercury discharge lamp (mercury lamp) that generates light such as i-line). This stepper has a projection lens that reduces the reticle pattern to 1/1.115, 1/10, etc. and projects it onto the wafer. distortion,
(magnification error, etc.), and fluctuations in imaging characteristics caused by the influence of usage conditions and environmental conditions can no longer be ignored.

For example, as disclosed in Japanese Patent Application Laid-Open No. 60-78454, one factor that changes the imaging characteristics of a projection lens is that when the exposure illumination light passes through the projection lens, the energy of the illumination light increases. Focusing on the fact that a portion of the image is absorbed by the projection lens, the fluctuation in imaging characteristics caused by that absorption,
In particular, it is known to calculate magnification errors and focus errors and correct them.

In this conventional technique, fluctuations in imaging characteristics are equivalently predicted by momentarily calculating the accumulation line of exposure energy that enters the projection lens via the reticle. In order to correct the fluctuations in the calculated imaging characteristics, a method is adopted that controls the pressure within the sealed air space within the projection lens, or a method that adjusts the mechanical distance between the projection lens and the reticle or wafer. has been done.

[Problem that the invention seeks to solve]

According to the above-mentioned prior art, it is possible to very well and stably correct fluctuations in imaging characteristics of a projection lens caused by partial absorption of exposure energy.

By the way, a stepper exposes multiple shot areas on one sheet of Ueno λ using a step-and-repeat method, so by shortening the exposure time for each shot HJI area, the processing time per sheet can be shortened. , efforts are being made to increase throughput. n Shortening of light time can be achieved by
Since the appropriate amount of exposure to be given to area I has been determined,
In practice, this is achieved by increasing the illuminance of the exposure illumination light.

However, as improvements are made to lighting systems and lamps to increase illuminance in order to improve throughput, the illumination system becomes too bright, and as a result, the amount of energy absorbed by the projection lens increases, resulting in This adversely affects various aberrations of the lens, and the excessive amount of accumulated energy causes problems such as insufficient correction of fluctuations in imaging characteristics. For this reason, the illuminance of the illumination light from the illumination system cannot be increased unilaterally, and a certain upper limit has been set based on the conditions specific to the projection lens.

One way to maintain this upper limit is to place a metallic filter for attenuating the light 11 in the illumination optical path from the lamp to the reticle at a position that is almost conjugate with the pupil of the projection lens, and to It has also been proposed to reduce the illuminance.

When such a filter is provided, the attenuation (transmittance) of the filter is such that the stepper is operated with the highest throughput exposure sequence (e.g., first print) using the reticle with the lowest pattern density of the available reticles. It was necessary to select an illumination intensity that would not cause the amount of stored energy in the projection lens to exceed the upper limit even when the projection lens was placed in a ribbed position.

However, reticles used in device manufacturing have various transmittances depending on the circuit pattern.

Here, the transmittance of a reticle means the ratio of the area of the transparent portion in the pattern area of the reticle that falls within the effective field of view of the projection lens or within a predetermined effective exposure area within the field of view.

For example, the transmittance of a reticle with a pattern for wiring is relatively high, about 30 to 60%, whereas the transmittance of a reticle with a pattern for contact holes is
It is extremely low, at around 3 to 6%, which is 1/I 0th place.

For this reason, for reticles with high transmittance for wiring layer exposure, the projection lens can be used efficiently close to its limit, but for reticles with low transmittance, the projection lens can be used well below the limit. There was a problem in that it ended up being used inefficiently.

Therefore, an object of the present invention is to improve the above-mentioned inefficient state and provide an exposure apparatus that improves the throughput of a reticle (mask) with low transmittance.

A further object of the present invention is to provide an exposure apparatus that optimizes exposure operating conditions according to the transmittance of a reticle (mask) and makes the apparatus more efficient to operate during device manufacturing.

[Means for Solving the Problems] First, in the present invention, an adjusting means is provided to vary the illuminance (illuminance per unit time) of exposure illumination light or energy rays on a mask or on an image plane. . Furthermore, a portion of the illumination light (energy rays) that enters the projection optical system (projection means) through the mask may accumulate in the projection optical system (average H product energy during exposure processing of one wafer). ! or the algebraic sum of the amount of incident energy and the amount of emitted energy that changes from time to time) is calculated based on the transmittance of the mask, the illuminance of the illumination light, or the exposure operating conditions. The illuminance of the illumination light is adjusted by the adjustment means so that the amount of energy multiplied by N in the projection optical system is equal to or less than a predetermined allowable amount of stored energy.

[Function] In the present invention, based on the phenomenon that the amount of energy accumulated in the projection optical system causes fluctuations in the imaging characteristics of the projection optical system, a value (information) corresponding to the amount of accumulated energy is obtained by predictive calculation. This allows the exposure operation to proceed so that the amount of stored energy is always below the allowable value. Therefore, when the transmittance of the mask or reticle is high, it operates to maintain the allowable amount of stored energy, and when the transmittance of the reticle is low, it operates to obtain the maximum illuminance within the allowable value. Therefore, the throughput of exposure processing using a reticle with low transmittance increases.

〔Example〕

FIG. 1 is a perspective view showing the configuration of a stepper according to a first embodiment of the present invention, and the basic configuration is disclosed in Japanese Patent Application Laid-Open No. 60-7845.
This is the same as that disclosed in Publication No. 4.

The mercury lamp l is arranged so that the light emitting point is located at the first focus of the elliptical mirror 2, and the illumination light focused by the elliptical mirror 2 is reflected by the gyroic mirror 3, which has a high reflectance in the short wavelength range. and is focused to the minimum diameter at the rotary shutter 4. The illumination light that has passed through the shutter 4 passes through a lens system 5 and a variable light quantity attenuation filter 6 and enters a fly's eye lens 7 as an optical integrator. A large number of secondary light source images are formed at the exit end of the fly-eye lens 7, and the light from each secondary light source is vertically reflected by a mirror 8, then enters a condenser lens 9, and is superimposed on a reticle R. be done.

Due to the effects of the fly's eye lens 7 and the condenser lens 9, the illuminance distribution of the illumination light on the reticle R becomes extremely uniform at a level of several percent or less.

Although not shown in FIG. 1, there is a gap between the fly-eye lens 7 and the condenser lens 9, for example
A relay system as disclosed in Japanese Patent No. 1-19129 is provided, and an image plane conjugate with the reticle R is created. A variable illumination field stop (reticle blind) that limits the illumination area according to the pattern area PA of the reticle R is arranged on this conjugate image plane.

In the direction, around the pattern area PA of the reticle R, various information regarding the reticle R (reticle name, pattern area PA
size, alignment mark position, etc.) are formed as a barcode BC.

Now, in the pattern area PA, a fine circuit pattern is formed with a light shielding material such as a chrome layer, and the illumination light that passes through the transparent part in the pattern is transmitted through the projection lens system 10 to the resist coating. It reaches the wafer W. The wafer W is placed on the wafer stage 1■ so that it is conjugate with the reticle R with respect to the projection lens 10! ! be placed. Wafer stage 11
moves two-dimensionally in the x1y direction, and its coordinate position is measured with high precision by a laser interferometer. In the case of second printing, a plurality of shot areas SA are formed in a matrix on the wafer W.

Further, the projection lens 10 is provided with a lens controller 12 for correcting imaging characteristics.

This lens controller 12 is based on Japanese Patent Application Laid-open No. 60784.
As disclosed in Japanese Patent Laid-Open No. 54 or 1981-19129, the magnification and focal position of the projection lens 10 itself are slightly corrected by pressure control, and the projection lens l
It has a function of correcting the distance between O and the wafer W by adjusting the offset of the focus sensor.

The main control system 20 controls basic operations such as the exposure sequence and alignment sequence of the stepper, and also performs calculations to optimally control the illuminance of the illumination light according to the transmittance of the reticle R.

The transmittance of the reticle R is detected by an illuminance sensor 21 provided on the wafer stage 11.

The light receiving surface of the illuminance sensor 21 has a size equal to or larger than the projected image (maximum effective exposure area) of the largest pattern area PA used, or includes a projected field of view (for example, a circle with a diameter of 23 m). The size is determined by

In addition, information regarding the transmittance of reticle R is stored in barcode B.
In the case of storing the reticle R in the reticle C, the barcode reader 22 that reads the barcode BC when loading the reticle R becomes a means for inputting the transmittance information.

Now, the main control system 20 receives a signal from the illuminance sensor 21,
Or based on the signal from the barcode reader 22,
A drive command corresponding to the optimum amount of attenuation is output to the drive system 23 of the attenuation filter 6. The main control system 20 also outputs a command to the power supply source 24 for driving the mercury lamp 1 to supply an appropriate power corresponding to the exposure sequence. This power supply source 24 checks the power supply based on a signal from a photoelectric sensor 25 that sequentially detects the illuminance (intensity) of light illuminating the reticle R.

In addition, the signal from the charging sensor 25 is set to 1 when the opening time of the shunter 4 is set to 1 on the automatic side in light intensity integration (integrator) mode.
If so, it is also input to the shank control system (not shown). The shutter control system exchanges information on the opening timing and opening timing of the shutter 4 with the main control system 20, and also sets the shutter 4 in timer mode (fixed time method) according to the set value from the main control system 20. It can also be controlled.

The console 26 is a man-machine interface between the operator and the stepper, and inputs and outputs various parameters and commands.

The lens controller 12 shown in FIG.
Various commands and information are exchanged with the control system 20 and with the shutter control system.

While the stepper is in operation, this lens controller 12 always performs correction control of the imaging characteristics of the projection lens 10, regardless of whether exposure processing is in progress. As disclosed in Japanese Patent No. 60-144938, a configuration that can operate with a flash exposure method in which the power supplied to the lamp l is temporarily increased from the nominal value only during exposure, or a normal exposure method in which the lamp is driven with the nominal power. It has become.

Figure 2 shows the attenuation filter 6 and drive system 23 in Figure 1.
, the lamp l, the power supply source 24, and an example of the configuration of the illuminance control calculation section in the main control system 20 are shown in a schematic diagram. A current detection circuit 24B that detects the current value flowing through the lamp 1, a voltage detection circuit 24C that detects the voltage value applied to the lamp 1, and a power calculation circuit that calculates the power supplied to the lamp 1 by multiplying the current value and the voltage value. 24D, an error amplification circuit 24B that calculates a deviation between a measured value Vm corresponding to the power supplied to the lamp 1 and a reference value Vr set from the outside, and performs feedback control of the power control element 24A so that this deviation becomes zero; It is provided as a basic configuration. Further, in this embodiment, a subtraction circuit 24H1 changeover switch 24J is provided to obtain the difference between the output signal S1 of the amplifier 24G1 which amplifies the signal of the photoelectric sensor 25, and the signal S1 output from the main control system 20.

The main control system 20 includes a data storage unit 20A that stores information regarding the magnitude of the signal S1, the transmittance η of the reticle R, various parameters of exposure operating conditions, a calculation unit 20B for illuminance control, and a lighting state of the lamp 1. A flash/normal control unit 20 that sets the timing and franchise embedding rate for setting the camera to a flash exposure method or a normal exposure method.
A stabilizing section 20D for stabilizing C1 and illuminance is provided. Furthermore, the attenuation filter 6 has four 74 routers 6a and H16c16d arranged on a disc-shaped plate,
It is possible to dim the illumination light by discretely switching it in four stages. Here, the filter 68 is simply a transparent part, and the light attenuation rate increases in the order of filters 6b, 6c, and 6d. The plate of the filter 6 is rotationally driven by a motor 6e under the control of a drive system 23.

Each filter 6a of this filter plate 6.

6b, 6c, and 6d are arranged in the illumination optical system at a position substantially conjugate with the pupil (entrance pupil) of the projection lens 1O, that is, at a position at the exit end of the fly's eye lens 7, or at a position substantially conjugate thereto.

Next, the operation of this embodiment will be described, assuming that in the stepper of this embodiment, the imaging characteristics are constantly corrected by the lens controller 12 shown in FIG.

[Earthwork] "j" ■L to 2■ First, the operator calculates the value Dos corresponding to the appropriate exposure amount for each shot, the number of exposure shots on one wafer W Ns,
Stepping time Tstp for each sit of the wafer stage 11 determined by the size of the sit area SA,
The average wafer exchange time Tc from the completion of exposure of one wafer until the next wafer is placed on stage 11, and for global alignment of the wafer W placed on stage 11, The average alignment time Ta1g required to detect the alignment mark on the wafer and align the first shot area on the wafer W with the reticle R is input from the console 26. Note that the alignment time Ta1g is zero at the time of first printing. Also, each time Tstp, Tc, T
a1g may be automatically set based on data actually measured in the past using a time counter provided in the stepper.

The data of each exposure operation condition mentioned above is stored in the data storage section 20A.
is stored as data Dexρ.

Next, the main control system 20 outputs a signal Ss from the stabilizing section 20D, switches the switch 24J from the state shown in the figure, makes the voltage Vd zero, and sets the flash/normal system i11 section 20 to zero.
A voltage Vp corresponding to the nominal power during normal exposure is output from C to the adding circuit 24F. Since the adder circuit 24F outputs ■=Vp as the reference value Vr, the lamp 1 is lit with an intensity corresponding to the nominal input power.
is controlled via the drive system 23 so that, for example, the filter 6a with an attenuation rate of zero is selected.

Next, the main control system 20 opens the shutter 4 in a state where the reticle R is not present or a plain glass is installed in place of the reticle. Position the stage 11 in advance.

In addition, the reticle blind is fully opened or opened to match the maximum effective exposure area. Then, the main control system 20 sets the output of the illumination sensor 21 at this time to P.

be memorized as

Next, as shown in FIG. 1, position the exposure reticle R, open the shutter 4 in the same way, and
The output from is stored as Pr.

Then, the main control B system 20 sets the transmittance η of the reticle R to Pr
/ P o and stores it in the data storage unit 2.
Store in OA. The transmittance η is in the range O<η<1.

Note that during this operation, the illuminance If of the illumination light received by the photoelectric sensor 25 (more precisely, the amount of illumination light on the reticle per unit time) is determined, and based on this illumination light amount If and the value Dos of the appropriate exposure amount. Average exposure time for one shot
p is calculated and stored in the data storage section 20A. The average exposure time Texp is calculated by Texp';Dos/If.

Next, the calculation unit 20B of the main control system 20 calculates the average amount of incident energy (average accumulated energy E) that enters (or passes through) the projection lens IO per unit time. Assuming that wafers are processed continuously, the incident energy is calculated based on the following equation (1) using the ratio of the total passing time of the illumination light to the processing time of one wafer, that is, the exposure time efficiency τ. Calculate IE.

E=η・If・τ+ΔE (1) Here, the energy amount ΔE per unit time is determined by the fact that part of the illumination light reflected by the wafer W enters the projection lens 10 during the exposure operation. This is the error caused by This energy amount ΔE is often quite small and can be ignored, but it may not be ignored in the case of a wafer with a high reflectance, for example, a wafer with an aluminum layer on the surface.

Furthermore, in this embodiment, for example,
It is assumed that the value Kw related to the reflectance of the wafer is determined by the method disclosed in the above publication. Therefore, if the illumination light beam per unit time on the wafer surface is K·If (K is a constant), the average energy amount ΔE per unit time is calculated by the formula (2)
).

ΔE=η・K−1f−Kw・τ ・・・・・・
(2) Therefore, by combining equations (1) and (2), equation (3) is obtained.

E−η・τ・If・ (−Kw to 1+)・・・・・・(
3) On the other hand, the exposure time efficiency τ is determined by each parameter Ns, Tc, TaJg, Tstp of the exposure operating conditions set at the beginning.
, T13Xl) using equation (4).

N s −Texp N s −(Texp+Tstp) + Ta1g
+Tc... (4) In this equation (4), the denominator is the total time required to process one wafer, and the numerator is the total exposure time for one wafer.

In addition, in equation (4), the illuminance of the illumination light (illumination light jiff
), the exposure time Texp will change, so equation (4) should be handled by the following equation (5).

Ns 0Texp+Tss In this equation (5), the time Tss is: Tss=N 5−Tstp +Ta1g +Tc −(
6) and can be considered a constant value.

The calculation unit 20B calculates the average amount of incident energy E by substituting the values of each parameter into the above equations (3) and (5).

Next, the fJ31E unit 20B determines the magnitude relationship (EmE) between the allowable average incident energy amount Em preset for the projection lens 10 and the calculated energy amount E.

Here, the allowable energy 1jl E m does not mean that if this value occurs even momentarily, it will immediately have a negative effect on the projection lens IO, but it is set considerably lower than the allowable value for the instantaneous amount of energy. . This allowable energy amount E m is determined in advance through experiments, etc., and
It is stored in OA.

As a result, the calculation unit 20B determines that the illuminance of the illumination light is to be reduced when Em-E<0.

Therefore, the fI calculation unit 20B calculates the filtration rate of the illumination light necessary for reducing the illuminance.

Therefore, the calculation unit 20B performs the calculation of equation (7), which is a combination of (3) and (5).

E Ifm η· (−Kw to 1+) Ns −Texp However, since n light time Texp is Texp−Dos/1r, equation (7) is transformed into equation (8).

Ifm η・(1+K・Kw) Ns 9 Dos When formula (8) is further summarized for illumination light Nff, it is transformed into formula (9).

(9) Therefore, the calculation unit 20B substitutes Em into equation (9), and also sets other constants η, K, Kw, and Ns.

By substituting Dos and Tss, the allowable illumination light amount 1fm corresponding to the allowable energy amount Em is calculated.

Here, if we calculate the ratio between the illumination light intensity I' calculated earlier and Ifm, If/I r m is the attenuation rate that should be calculated. Select filter 6 with .

The attenuation factors of the three filters 6 b s 6 c and 6 d for the filter 6 a are stored in advance in the data storage unit 20A. Therefore, an attenuation filter that is not smaller than the calculated I f71fm and as close to r f/1fm as possible is selected.

As a result, the calculation unit 20B outputs a signal St representing the selected filter to the drive system 23.

Next, the main control system 20 controls the illumination light 11fc per unit time on the reticle obtained under the selected attenuation filter.
Calculate 0 If the attenuation rate of the selected filter for filter 6a is αC, then I r c = ac - I f
...(10).

Since this illumination light amount 1fc becomes the illuminance on the reticle in the actual exposure operation, the calculation unit 20B calculates the exposure time Texp among the parameters of the exposure operation conditions, Texp =
It is corrected by the Dos/Ifc calculation and stored in the data storage unit 2OA. However, when the exposure amount control is in integrator mode, the opening time of the shutter 4 (n light time Texp) is automatically corrected according to the illumination light amount Ifc, so there is no need to correct the exposure time Texp. However, in the timer mode, the shutter 4 is opened for the corrected exposure time Texp. For completeness, when in timer mode, it is also possible to actually measure the illuminance after attenuation and confirm the attenuation line before proceeding with the exposure operation. As each parameter of the exposure operation conditions is determined as described above, the main control system 20 sequentially exposes the wafer W according to the exposure sequence.In addition, in FIG. 2, when the parameters necessary for exposure are modified, The corrected data is output from the calculation unit 20B as Dchg.

As described above, in this operation, when actually measuring the transmittance η of the reticle R, the flash/normal control section 20C outputs the voltage Vp corresponding to normal exposure. However, when the actual exposure operation is performed by flash exposure, the calculation unit 20B transmits the signal S3 to the flash/normal control unit 20C so that a voltage Vp corresponding to approximately twice the nominal input power of the lamp 1 is output. Output to. Furthermore, when information on the transmittance l is input from the barcode reader 22 or when the operator inputs it from the console 26, it goes without saying that actual measurement using the illuminance sensor 21 is not necessary. is small, there are cases where the filter plate 6 is set to the filter 68 with a zero attenuation rate in the flash exposure mode.

In this case, the amount of illumination light on the reticle R corresponds to the maximum illuminance that the illumination system can output, and even in that state, the allowable energy f! If it does not exceed 1E m, exposure is performed as is.

In this embodiment, a filter with a four-stage light attenuation rate was used, but a similar effect can be obtained with a stepper using a filter that can switch the illuminance to two stages.

In the first operation mode, the light intensity of the lamp 1 is switched in two stages by switching between flash exposure and normal exposure, and the attenuation rate is switched in four stages by the filter 6. Adjustment was possible. Therefore, in most cases, the average incident energy amount E during actual exposure is kept low compared to the allowable average incident energy amount Em. Therefore, an exposure operation in which the average amount of incident energy E is brought as close to Em as possible will be described below with reference to FIG.

The basic operation is the same as the first operation mode, and the formula (
3), (5), and (9), allowable energy amount Em
Find the illumination light amount 1fm corresponding to .

As shown in FIG. 3, for example, if the illumination light beam when the filter 6a (attenuation rate is zero) is set to normal exposure mode is If, and the illumination light beam when set to flash exposure mode is If, then the calculation is made. The allowable illumination light amount 1fm is If
, the illuminance cannot be increased any further.

On the other hand, when the allowable illumination light 11fm is between If and If, the light emission intensity of the lamp 1 can be adjusted while the filter is set to 6a.

The actual measured value of this illumination light 111f, or 1 ft, is detected by the photoelectric sensor 25 and stored in the data storage unit 20A, so the calculation unit 20B performs a correction calculation for the voltage Vp applied to the addition circuit 24F. , if the voltage Vp in flash mode is VP+, then the third
As shown in the figure, the voltage Vp for obtaining the allowable illumination light ill f m is determined by the following equation (11).

V p =Vp+ AVP+=VGl+' (I
fll/Tf+) (11) In the normal mode, it is similarly calculated using equation (12).

V P ”Vpt+ΔVpt-Vρz ・ (Ifm/
Ih) And the calculation unit 20B is a flash normal system? A signal S corresponding to the calculated new voltage Vp is output to the first section 20C. As a result, the lamp 1 is driven in a flash mode (lit with a power greater than the nominal rated power only while the shutter 4 is open) so that an illuminance approximately equal to the allowable illumination light 111fm is obtained during actual exposure.

Next, the allowable illumination light amount 1fm calculated when the attenuation by the filter 6 is zero is equal to the illumination light ff1 during normal exposure.
The case where l f is lower than 0 is explained with reference to Figure 4.0 When a normal mercury lamp is driven with a power lower than the rated input power, the discharge becomes unstable or the discharge stops. Therefore, it is necessary to avoid driving the lamp 1 with lower power than the rated power. So in this case,
Control is performed in combination with attenuation by filter 6.

First, as shown in FIG. 4, check the control range by adjusting the supply power of the illumination light amount that changes by switching the filter 6. For example, set the attenuation rate of the filter 6a to zero (transmittance β is 1.0), and set the attenuation rate of the filter 6a to zero (transmittance β is 1.0). Reduce the attenuation rate to 20% (
β-0,8), the attenuation rate of filter 6C is set to 40% (β-0,8)
-〇, 6) and the attenuation rate of filter 6d is set to 60% (β
= 0.4), the allowable illumination light amount 1 r m is
When the transmittance β of the filter is 0.6 or 0.4,
It can be seen that it is within the control range. Therefore, the calculation section 20B
is a filter 60 with an attenuation rate of 40% (β = 0.6)
Select and set. At the same time, the calculation unit 20B calculates the upper limit β·I'6 or the lower limit β·If2 of the control range.The calculation unit 20B calculates the target illumination light amount 1fr from the relationship of the following equation (13).

lfm Ifr [fm
Tfr (13) This target illumination light amount 1 r r corresponds to the illuminance that should be obtained on the reticle when the attenuation by the filter 6 is zero. As is clear from this equation (13),
If an appropriate attenuation factor (transmittance β) is determined, Ifr becomes Irr
=Irm/β. Further, Irr is always set to +rz<I f r<l f.

After that, ifr is added to Irm in equation (11) or (12),
By substituting , the voltage Vp corresponding to the lamp supply power is determined by the following calculation.

As described above, in the second operation mode, since the projection lens can be used at the very limit determined by the allowable average incident energy 11Em, there is an advantage that the efficiency in terms of exposure sequence is maximized.

[3. Mode' This operation mode uses the stabilizing section 20D in the main control system 20 to stabilize the light emission intensity of the lamp l to a constant value. Generally, the emission intensity of a mercury lamp changes depending on the input power, but its linearity is not very good.Therefore, the illuminance on the reticle during exposure is detected by the photoelectric sensor 25, and a voltage is applied to compensate for the change in the emission intensity of the lamp 1. Vd is generated by the amplifier 24G, the il calculating circuit 24H1, and the stabilizing section 200, and this voltage Vd is added to the voltage Vp by the adding circuit 24F to stabilize the light emission intensity of the lamp 1. In this case, in the normal exposure mode, the switch 24J is fixed at the position shown in FIG. 2, but in the flash exposure mode, the switch 24J is fixed only when the shutter 4 is open.
J to the position shown in Figure 2, and switch 2 during other non-exposure periods.
4J is switched to earth by the signal S.

Now, for example, using the method explained earlier, the allowable illumination light amount is 1 fm.
is determined, the calculation unit 20B calculates that the amplifier 24G has the allowable illumination light amount! The magnitude of the signal S1 to be output when rm is calculated, and the value is sent to the stabilizing section 20D as the signal S4. When attenuation is performed by the filter 6, the stabilizing unit 20D corrects the amplification factor of the subtracting circuit 24H according to the attenuation factor (transmittance β), and also uses the value inputted as the signal S4 as the signal S in the subtracting circuit. Apply to 24H.

The subtraction circuit 24H calculates the voltage Vd using the following equation (14) while the photoelectric sensor 25 is receiving illumination light.

va-(5431)/β (14) Therefore, the reference value V' which determines the power supplied to the lamp l during one shot exposure operation is expressed by equation (15).

Vr=Vp+Vd=Vp+(36-S+)/β...
(15) Therefore, for example, the emission intensity of the lamp 1 is the illumination light 11 f
When increasing from the value corresponding to m, the voltage Vd changes in the negative direction, lowering the reference value V'.
The light emission intensity decreases, and feedback control is performed to always maintain a constant light emission intensity.

As described above, in the first embodiment of the present invention, a discrete filter 6 is used as the illuminance attenuation filter 6, but it goes without saying that a continuously variable filter 6 may also be used. The one that makes the aperture diameter variable is the light source image (fly's eye lens 7) formed on the pupil plane of the projection lens IO.
This is not preferable because it may change the size of the light source image at the exit end of the wafer, and the numerical aperture (N, A, It is best to use a filter that reduces the light without changing the diameter (diameter on the surface).Also, if you use a metal plate or ceramic plate with randomly arranged micropores, or a metal mesh, it will be better to use a filter that reduces the light intensity. This is advantageous because it can withstand high temperatures caused by the irradiation of strong illumination light from 1. Alternatively, one filter or a plurality of filters may be combined, and the number of combinations may be automatically switched.

Furthermore, the exposure time efficiency τ described in this embodiment needs to be optimally calculated depending on the wafer processing sequence of the stepper. In particular, in the case of the Gui-Pai-Gui (or site-pie-sight) method in which marks are detected and aligned for each shot area SA on the wafer W, the alignment time for each shot is T a 1 g
t % global alignment time T a I g
+, the above equation (6) becomes equation (6a).

Tss=Ns(Tstp +Ta1gg) +Ta1g
++Tc... (6a) Next, a second embodiment of the present invention will be described with reference to FIG. The difference from the first embodiment is that whether or not the allowable average incident energy amount Em is reached is determined from the characteristic variation predicted value calculated by the lens controller 12. The method shown in FIG. 5 is the same as the method disclosed in Japanese Patent Application Laid-Open No. 63-58349.

Now, in FIG. 5, time 1. ．． 1.・・・・・・１１
) represents a sampling time every fixed time Δt (2 mSec to 5 Sec), and the lens controller 12 calculates the amount of energy ΔQ incident on the projection lens 10 during the time Δt.
is obtained by equation (16).

ΔQ=rt-1f・Δt・(-Kw to 1+)・D
u (16) Here, Du is the ratio of the total open time of the shunter 4 within Δ. Then, using the predicted value Yn at the sampling time Ln, the predicted value Y□ at l at the next time after Δ is determined. Here, if the attenuation rate of the characteristic fluctuation unique to the projection lens (the rate at which the fluctuation value changes from the initial value during Δ) is CL (0<Ct<1), the lens controller 12 calculates equation (17). do.

Ya−+ = Ct (Y n+ΔQ) ・・・・・・
(17) Thereafter, the lens controller 12 calculates equation (17) every time Δ passes (thereby obtaining real-time change characteristics of the amount of incident energy).

Then, according to this change characteristic, the fluctuations in magnification and focus are corrected. So, for example, up to time t, if the amount of incident energy ΔQ between 61 and 61 is ΔQ1, then the main control system 2
0 monitors the predicted value Yn at each sampling time,
It is determined whether or not the allowable average incident energy amount Em exceeds a permissible value Ym determined corresponding to the permissible average incident energy amount Em. In FIG. 5, the main control system 20 determines that the permissible value Ym is exceeded at the time .
After time L6, illumination light 11 per unit time on the reticle
1f is lowered by a neutral density filter 6 or lamp control. Of course, along with this, the exposure time Texp is also slightly longer (and therefore, from the next sampling time, ΔQ (ΔQt<ΔQ) is used as the new amount of incident energy.

As a result, the predicted value changes from the characteristic Ca to the characteristic cb, and is kept below the allowable value Ym. Furthermore, the fifth
In the figure, since no exposure is performed after time t1, the predicted values Y0 and Yll monotonically decrease.

As described above, according to this embodiment, the limit value regarding the amount of energy of the projection lens is determined based on the predicted value of the amount of incident (accumulated) energy calculated in almost real time.
Even during exposure processing of one wafer, the projection lens can be used to its limit. Note that the illuminance adjustment limit value or illuminance adjustment line may be determined based on the balance between the allowable average incident energy amount Em determined in the first embodiment and the allowable value Ym determined in this embodiment.

Furthermore, if the illuminance is changed during the exposure operation of one wafer, tr will change in the calculation of equation (16). It is sufficient to provide an integrating circuit that integrates the signal Sl from Δt only for a period of Δt, and use the integrated value in place of If, Δ, and Du in equation (16).

In the first and second embodiments of the present invention, a stepper that uses a mercury lamp has been described above, but a stepper that uses an excimer laser source that generates a powerful laser beam in the ultraviolet region as a light source can also have the same effect. can get.

In the case of an excimer laser, since it is a pulse oscillation, it is only necessary to adjust the light N (for example, peak value) and pulse interval (oscillation period) for each pulse, and it is necessary to accurately know the attenuation rate of the filter 6. When the illuminance sensor 21 on the wafer stage 11 is used without the reticle R,
The attenuation rate can be found extremely easily. Furthermore, in each embodiment, the transmittance caused by the roughness of the reticle pattern, the presence or absence of transparent parts, etc. was discussed, but since the contrast of the pattern itself is intermediate in an emulsion mask etc., the illuminance sensor 21 (4 degrees) will be measured. The present invention can be similarly applied to this emulsion mask.

Incidentally, in each of the embodiments, a stepper is used as an example, but similar effects can be obtained with a batch exposure apparatus using a mirror projection aligner using a projection optical system and a 1-1 magnification projection lens. Further, the present invention can also take measures against the thermal influence of a mask using the same concept for X-ray exposure equipment. FIG. 6 shows the configuration of a typical X-ray exposure apparatus, in which X-rays IB from an X-ray source IA reach a wafer W arranged in a proximity gamble through a pattern area PA of a mask M. The mask M generally consists of a frame Mf hollowed out in the center of a silicon substrate, and a thin film (1 to 5 μm thick) Ms such as polyimide stretched over the lower surface of the frame Ml, and the pattern area PA is formed on the thin film Ms. It is formed by vapor depositing an X-ray absorber such as metal. In this case, the X-ray source IA is SO
When strong X-rays IB such as R are generated, the temperature of the metal layer in the pattern area PA changes due to absorption of the X-rays. Therefore, the pattern area PA undergoes thermal expansion, and the pattern surface of the mask M loses its flatness. Therefore, either a filter 6A is provided to reduce the illuminance of the X-ray IB, or
A system for controlling the rAIA is provided to suppress the illuminance of the X-rays irradiated to the mask M to such an extent that the influence of thermal expansion does not occur. Since the thermal expansion of the mask M corresponds to the area of the metal layer in the pattern area PA, an X-ray sensor 21A is provided on the wafer stage 18 to measure the transmittance (or concentration) of the mask MOX rays and determine the tolerance. If it exceeds the value, filter 6
Just insert A.

[Effects of the Invention] As described above, according to the present invention, the influence caused by the accumulation of energy of illumination light (energy rays) in the projection optical system or the mask can be substantially eliminated, regardless of the difference in the transmittance or absorption rate of the mask. It is possible to approach a constant value, to manufacture semiconductors with extremely high yield, and to greatly improve the efficiency of the exposure sequence.

[Explanation of symbols of main parts]

l...Lamp 4...Shutter 6...Darkness filter 10... Projection lens 12... Lens controller 20... Main control system 2I... illuminance sensor 23... Drive system 24...Power supply source 25...Photoelectric sensor R...Reticle W...Wafer Debetsu person Nikon Co., Ltd.

Claims (2)

[Claims] (1) In an apparatus that irradiates a predetermined area on a mask with illumination light and exposes an image of a pattern formed in the predetermined area onto a sensitive substrate via a projection optical system, part of the illumination light passes through the mask. input means for inputting first information corresponding to the energy amount of the illumination light incident on the projection optical system; calculation means for calculating in advance second information regarding time efficiency, and calculating in advance third information regarding the amount of energy that can be stored in the projection optical system based on the second information and the first information; ; illuminance adjustment means that compares fourth information regarding the allowable storage energy amount of the projection optical system set in advance with the third information, and adjusts the illuminance of the illumination light based on the comparison result; An exposure device characterized by: (2) An energy source that irradiates a predetermined area on a mask with energy rays, and a projection that has a property of absorbing a portion of the energy rays and projects a pattern formed within the predetermined area of the mask onto a sensitive substrate. In the exposure apparatus equipped with means, a first value corresponding to the amount of energy that can be stored in the projection means is calculated based on predetermined exposure operating conditions and a value corresponding to the illuminance of the energy ray, and calculation means for calculating a magnitude relationship between a second value corresponding to a set allowable storage energy amount; and based on the calculation result, the first value is calculated within a range permitted by the energy source or the exposure operation conditions; an exposure apparatus comprising: adjusting means for adjusting the illuminance of the energy ray so that the value of is maximized below the second value.