JP3316850B2 - Energy control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to control of irradiation energy amount to a sensitive object, and particularly to total irradiation when the energy amount from a pulse oscillation type energy source has a temporal change. The present invention relates to control of an energy amount, for example, to an energy amount control device suitable for controlling an exposure amount of an exposure apparatus that uses a pulse laser such as an excimer as exposure light.

[Conventional technology]

In an exposure apparatus (stepper, aligner, etc.) using a pulse laser as a light source used in a lithography process for manufacturing semiconductor devices, the laser light generally has a variation of about ± 10% for each pulse, and the exposure surface (reticle or On the wafer), a regular interference pattern due to the coherence of the laser light, and an irregular interference pattern in which a large number of light beams having different phases caused by scratches, dust, surface defects, etc. in the illumination optical system are overlapped. Speckles), which may cause uneven illuminance on the exposed surface.

The above two interference patterns, especially regular interference patterns, have a significant effect on the control of the pattern line width in the photolithography process of manufacturing a semiconductor device. For example, Japanese Patent Application Laid-Open No. 59-226317 or Japanese Patent Application Laid-Open
It is also considered to smooth regular interference patterns and speckles (hereinafter collectively referred to as interference patterns) by a method equivalent to the method disclosed in Japanese Patent No. 259533. The smoothing (incoherence) of the interference pattern disclosed in the above publication is performed by moving the laser beam one-dimensionally or two-dimensionally (raster scan) at a fixed period by a vibrating mirror (galvano mirror, polygon mirror), and spatially. This is to reduce coherency. In other words, the interference pattern is moved on the reticle by changing the incident angle of the laser beam to the illuminance equalizing means (optical integrator) for each pulse, and finally the interference pattern is smoothed, in other words, the illuminance This is to improve uniformity. At this time, a plurality of pulses are emitted in synchronization with one-dimensional or two-dimensional scanning by the vibrating mirror. Normally, the oscillation pulse width of an excimer laser is extremely short, about 20 nsec. Even if the oscillating mirror is oscillated at about 10 Hz, one pulse of the excimer laser behaves as if it is stationary during the oscillation cycle of the oscillating mirror.

Therefore, in order to achieve the smoothing of the interference pattern by a plurality of pulses (uniform illuminance) and the desired exposure amount control accuracy, (1) the energy amount per pulse is kept substantially constant during the exposure; 2) It is important to obtain a target exposure with an integer multiple of the half cycle of the mirror oscillation in one-dimensional or two-dimensional scanning by the oscillation mirror.

[Problems to be solved by the invention]

By the way, the laser light has a variation of about ± 10% for each pulse, and there is a phenomenon that the laser density decreases in a short term and a long term. This phenomenon of a decrease in laser density is particularly remarkable in a gas laser, in which the output decreases with the deterioration of a mixed gas of an active medium (for example, KrF, XeCl, or the like) sealed inside the chamber. In general, when the relationship between the applied voltage to the pulse laser light source and the energy amount of a pulse emitted under the applied voltage (hereinafter simply referred to as oscillation energy amount) changes over time, for example, the gas laser If the output of the laser light source decreases with the deterioration of the mixed gas of the active medium, a desired oscillation energy amount can be obtained even if the applied voltage corresponding to the pulse energy amount to be emitted next is determined from the above relationship. I couldn't do that. Generally, a laser light source has a constant applied voltage mode and a constant energy amount mode. Especially when the output decreases due to gas deterioration in the constant energy mode,
Conventionally, based on the output of a monitor unit that receives a part of a laser beam and detects the amount of energy, a voltage applied between two electrodes inside a chamber is gradually increased to reduce a decrease in output. Something has been devised. However, in the above-described energy amount control, a constant oscillation energy amount is always obtained, but a desired oscillation energy amount (that is, an applied voltage corresponding to the oscillation energy amount) is obtained in the entire range of a predetermined energy amount control range. Can not,
In other words, there has been a problem that accurate fine adjustment of the oscillation energy amount cannot be performed for each pulse, and high-precision energy amount control cannot be achieved.

The present invention has been made in consideration of the above points, and achieves high-precision energy amount control by adjusting the applied voltage even when the relationship between the applied voltage and the oscillation energy amount in the energy generation source changes over time. It is an object of the present invention to obtain an energy amount control device capable of performing the above.

[Means for solving the problem]

In order to solve such a problem, the present invention includes an energy source 1 that emits pulse energy with energy fluctuation within a predetermined range every time oscillation occurs, and adjusts a voltage applied to the energy source 1 by
In an apparatus for controlling the energy amount of pulse energy, storage means for storing information on a relationship between an applied voltage to the energy source 1 and an energy amount of pulse energy emitted from the energy source 1 under the applied voltage. [Memory 7]; energy amount measuring means for detecting the energy amount of pulse energy actually emitted from the energy generation source 1 [energy monitoring element 4
And an energy amount monitoring unit 5 or a light receiving element 4 ′ and a light amount monitoring unit 5 ′]; an applied voltage applied to the energy generation source 1 for each predetermined number of pulses or for each unit time; Calculating means [arithmetic unit 6] for updating the information on the relationship between the applied voltage and the energy amount stored in the storage means based on the energy amount detected in [1]; and based on the information updated by the arithmetic means. ,
A determination means (calculator 6) for determining an applied voltage to the energy generation source 1 corresponding to the energy amount of the pulse energy to be emitted next is provided.

(Operation)

In the present invention, data relating to the applied voltage to the energy generation source (or the actual charging voltage at the time of energy oscillation) and the amount of oscillation energy are fetched for each unit pulse or unit time, and the applied voltage stored in the storage means in advance is stored. The relational expression between the energy and the oscillation energy is sequentially updated by calculation. For this reason, even if the relationship between the applied voltage or the charging voltage and the oscillation energy amount changes over time, the relational expression expressing the change is appropriately updated according to the change over time, so that good energy amount control is always achieved. It becomes possible.

〔Example〕

FIG. 1 is a block diagram showing a schematic configuration of an energy amount control device according to a first embodiment of the present invention. Here, in order to obtain the simplest and basic configuration, an input from an input / output device 8 is performed. In accordance with the specified oscillation condition, pulse energy oscillated from the pulse oscillation type energy generation source 1 is applied to the irradiation target 3.

In FIG. 1, an applied voltage control section 11 controls a high-voltage discharge voltage (corresponding to an applied voltage) of a pulse oscillation type energy generating source 1, and applies an applied voltage corresponding to an energy amount of pulse energy to be irradiated next. By applying a voltage to the energy generation source 1, the amount of energy is adjusted for each pulse. After a predetermined charging time required by the energy generation source 1 has elapsed, the trigger control unit 10 sends an external trigger pulse to the energy generation source 1 to control its oscillation (number of pulses, oscillation interval, and the like). Here, the trigger control unit 10 and the applied voltage control unit 11 are both connected to the main control system 9 (described later).
It operates in response to a predetermined command output from. The pulse energy oscillated from the energy generation source 1 may be any coherent laser light, non-coherent pulse light, or pulse energy other than light such as an electron beam.

The energy beam EB emitted from the energy source 1 is split by the beam splitter 2, and most of the energy beam EB passes through the beam and irradiates the irradiated object 3. On the other hand, part of the energy beam EB reflected by the beam splitter 2 is
(For example, in the case of an excimer laser, a pyroelectric power meter, a PIN photodiode, or the like), and the monitor element 4 accurately outputs a signal corresponding to the energy amount of each pulse of the energy beam EB. The output signal from the monitor element 4 is input to an energy amount monitor 5, where it is converted into an energy amount for each pulse. Therefore, the monitor element 4 and the energy amount monitoring unit 5 constitute an energy amount measuring means of the present invention, and are associated with the energy beam irradiated on the irradiation target 3 in a predetermined relationship, that is, the optical performance of the beam splitter 2. The energy amount of the energy beam uniquely determined by is measured.

The actually measured value measured by the energy amount monitoring unit 5 (the value may be any value corresponding to the actually measured energy amount and does not need to be the energy amount itself) is sent to the arithmetic unit 6, where the energy of each pulse is calculated. While the amounts are sequentially accumulated, the arithmetic unit 6 applies the applied voltage to the energy generating source 1 and the amount of oscillation energy under the applied voltage or the actual amount of energy given to the irradiation target 3 (so-called dose amount). The information about the relationship with is updated (details will be described later).
Note that the relationship between the actual energy amount of the energy beam and the sensitivity of the monitor element 4 is determined in advance by the power meter for the monitor element 4 and stored in the memory 7. Instead of calculating the integrated energy amount by the arithmetic unit 6, the energy amount for each pulse may be sequentially integrated in the energy amount monitoring unit 5. In this case, the oscillation energy amount and the integrated energy amount for each pulse are calculated. Output to arithmetic unit 6.

The arithmetic unit 6 includes arithmetic means for updating the relationship between the applied voltage and the amount of oscillation energy (or dose) according to the present invention, and stores the above information stored in the memory 7, the applied voltage during the oscillation of the previous pulse, and the energy. The oscillation energy amount from the amount monitor unit 5 is taken in, and based on these data,
The information regarding the relationship between the applied voltage and the oscillation energy amount is updated according to a predetermined calculation process, and stored in the memory 7 (details will be described later). Further, the computing unit 6 also includes means for determining an applied voltage in the present invention, and based on the integrated energy amount obtained by sequentially integrating the oscillation energy amounts detected by the energy amount monitoring unit 5 for each pulse, a predetermined energy amount is calculated. The energy amount of the energy beam to be irradiated next is obtained according to the control logic (described later). Then, the arithmetic unit 6 calculates the relationship between the updated applied voltage and the oscillation energy amount,
Next, the applied voltage corresponding to the amount of pulse energy to be irradiated is determined by calculation and sent to the main control system 9.

The main control system 9 outputs the applied voltage and the command signal of the oscillation trigger pulse determined by the computing unit 6 to each of the applied voltage control 11 and the trigger control unit 10. The input / output device 8 receives various parameters required for oscillation from the operator, and notifies the operator of the energy amount of the final pulse as necessary. The memory 7 stores parameters (constants), tables, and the like necessary for the oscillating operation, various calculations, and the like input from the input / output device 8.

Here, in FIG. 1, means for detecting the charging voltage between the two electrodes during energy oscillation in the energy generation source 1 (which uniquely corresponds to the applied voltage applied to the energy generation source 1) ( The charging voltage measuring means of the present invention is not shown, and the present embodiment describes a case where there is no charging voltage measuring means. Energy source 1
In the case where the charging voltage measuring means is provided, the calculation result by the charging voltage measuring means is taken into the calculating means 6 and the information on the relationship between the charging voltage and the oscillation energy amount can be updated instead of the applied voltage. Then, the description is omitted.

Next, a method of updating information relating to the relationship between the applied voltage and the oscillation energy amount, which is the center of the present invention, will be described in detail.
FIG. 2 is a diagram showing an example of the relationship between the applied voltage and the energy amount of the ejection pulse, and has a quadratic function here. In FIG. 2, the black circles are actual data,
The solid line is a curve obtained by fitting the data as a quadratic function by the least square method. Therefore, fitting of a quadratic function by the least squares method will be described. In this embodiment, the least squares method is used for fitting a quadratic function. However, other than the least squares method described below, for example, a method of minimizing the maximum deviation from data may be adopted. Therefore, if the applied voltage is V and the pulse energy amount is P, the model function is expressed by the following equation.

P = a + bV + cV ² (1) where a, b, and c are unknowns determined by the least squares method. Next, respective data regarding the actual applied voltage and the pulse energy amount are set as V _i and P _i . The subscript i represents the newness of the data, i = 1 being the latest data, and the data becomes past data as i increases. Further, the evaluation function E
To far. Here, γ _i is a weight (described later) for the data (V _i , P _i ). Now, the unknowns a, b, and c that minimize the evaluation function E are calculated according to the least squares theory. By solving the following ternary simultaneous equations, it can be obtained from the following equation.

However, By the way, γ _i is a weight for the data (V _i , P _i ). As described above, the relationship between the applied voltage V and the oscillation energy amount P gradually changes in accordance with the change over time (for a gas laser, the deterioration of the mixed gas inside the chamber).
For this reason, by setting the weight γ _i to γ ₁ > γ ₂ > γ ₃ ..., It is necessary to make the weight of the latest data the heaviest and to gradually reduce the weight as the data becomes older. Therefore, the weight γ _i is defined as in the following equation.

γ _i = ε ^i-1 (4) Here, ε is a constant satisfying 0 <ε <1, and specifically, a rate of change of the relationship between the applied voltage V and the oscillation energy amount P over time. Is a value determined in advance in accordance with. For example, when ε is set to 0.995, the contribution (weight) of the data (V _i , P _i ) regarding the oscillation pulse about 920 times before to the evaluation function E is obtained.
Is about 1% of the latest pulse. Therefore, the constant ε
Approaching 1, the unknowns a to c are determined from a large number of data (V _i , P _i ) as is apparent from the above equation (3), and the variation in energy amount for each pulse is determined. (About ± 10%) can be prevented from lowering the detection accuracy of the unknowns a to c. However, if the relationship between the applied voltage V and the oscillation energy amount P fluctuates more than the above-mentioned fluctuation due to any cause, the fluctuation is delayed due to the large number of past data (V _i , P _i ). It may be difficult to follow and calculate the unknowns a to c without any change. When brought close to the value of the constant ε 0 Conversely, a slight data (V _i, P
_The unknowns a to c are determined from _i ), and the followability to the change in the above relationship is improved, but the influence of the variation in the energy amount for each pulse is greatly affected.
Therefore, in practice, it is desirable to determine the value of the constant ε by experiment in consideration of the balance between the two according to the stability of the energy generation source 1 and the like.

Next, each element of the matrix on the right side of the above equation (3) is Each of the above-mentioned elements, that is, parameters C _{1 to} C ₅ , D ₁ , is used as information on the relationship between the applied voltage V and the oscillation energy amount P.
DD ₃ are stored in the memory 7. Then, when new data (V _i , P _i ), that is, the latest data (V ₁ , P ₁ ) is obtained, the arithmetic unit 6 stores the parameters C _{1 to} C ₅ and D _{1 to} D ₃ from the memory 7.
Except for the constant C ₁ (C ₁ = 1 / (1−ε ² )), the parameters C _{2 to} C ₅ and D _{1 to} D ₃ are obtained by the following recurrence formula.
Shall be updated. As a result, by applying the recurrence formula, the operation time required for updating the information on the relationship between the applied voltage V and the oscillation energy amount P can be shortened, and the arithmetic unit 6 newly stores the updated information in the memory 7. Will do.

By the way, if the above-mentioned equation (1) is solved for the applied voltage V and only the solution satisfying V ≧ 0 is adopted, the following equation is obtained.

Therefore, every unit pulse number or every certain time. Parameters are updated appropriately in the above _{(6) C 1 ~C 5,} D 1 ~D 3
When the unknowns a to c are obtained by calculating Expression (3) from Equation (3), the relational expression (Expression (1)) between the applied voltage V and the oscillation energy amount P is updated, and further, the predetermined energy amount control is performed by Expression (7). The applied voltage V corresponding to the oscillation energy amount P of the next pulse determined under the logic can be obtained.

Next, an example of the energy amount control logic of the present embodiment will be described. The target integrated energy amount to be given to the irradiation target 3 by irradiation of a plurality of pulses is S ₀ , the required energy amount control accuracy is A ₀ (however, 0 <A ₀ <1), and a pulse with the same applied voltage If the variation in the amount of oscillation energy between ΔP (eg, ΔP / P = about 10%) and the amount of oscillation energy corresponding to the maximum applied voltage Vmax in the above equation (1) is Pmax (maximum value), energy P ₁ eye pulse energy is determined from the following equation.

When the energy amount of the _k-th pulse is set to P _k , the integrated energy amount (actually measured value) I _j up to the j-th pulse energy is And the (j + 1) -th pulse energy amount P _{j + 1}
Is determined from the following equation. Note that min (σ, ρ) is σ,
This means that the smaller value of ρ is adopted.

This energy amount control logic of energy control dynamic range (i.e., adjustment range of the applied voltage V) although large, if there is no target integrated energy amount S ₀ is much larger than the maximum pulse energy amount Pmax, only a small number of pulses Has the advantage that a desired amount of irradiation energy can be obtained.

Next, the operation of this embodiment will be described with reference to FIG. FIG. 3 is a schematic flowchart showing an example of the operation of the present embodiment. In step 100, it is determined whether or not to initialize the parameters _{C 1 ~C 5, D 1 ~D} 3 is information about the relationship between the applied voltage V stored in the memory 7 and the oscillation energy amount P. This may be determined by the operator or automatically performed according to a predetermined program. In the energy control apparatus shown in FIG. 1, the computing unit 6 actually determines whether or not to initialize based on the oscillation stop time of the energy generation source 1 and the like, and the energy generation source 1 keeps oscillating. If, shorter its stopping time even if the oscillation is not stopped, when the parameter _{C 1 ~C 5, D 1 ~D} 3 in the memory 7 can be sufficiently reliable, the process proceeds to step 103. On the other hand, when initialization is necessary, for example, when the energy generation source 1 is started up or its oscillation has been stopped for a long time, the process proceeds to step 101, where the applied voltage V is sequentially changed, and The pulse energy amount P for each pulse oscillated by (1) and (2) is fetched from the energy amount monitoring unit 5, and the relationship shown in FIG. The measurement operation in this step is completed in a short time, and the output of the pulse energy does not decrease due to a change with time during the operation. The operation here is programmed in advance and performed automatically. Calculator 6 in the next step 102, based on the data obtained in step 101 (V _i, P _i), and calculates a parameter _{C 1 ~C 5, D 1 ~D} 3 from equation (6), the memory 7 is stored.

In the next step 103, the arithmetic unit 6 sets the input / output device 8
Integrated energy amount S ₀ given from the above, the energy amount control accuracy A ₀ stored in the memory 7, the pulse energy variation between pulses (ΔP / P), and the maximum applied voltage Vma
Take x and The variation (ΔP / P) is calculated in the previous step.
It may be a value obtained from the actual data (V _i , P _i ) obtained in 101. Then, the computing unit 6 determines the _first pulse energy amount P1 according to the equation (8), calculates the equation (7) from the unknowns a to c obtained by the equation (3), and calculates the first pulse energy amount P1. calculates the applied voltages V ₁ corresponding to the eyes of the pulse energy P ₁ (step 104). Thereafter, the main control system 9 supplies a command signal corresponding to the calculation result of the arithmetic unit 6 to the applied voltage control unit 11 and the trigger control unit 10, and the applied voltage control unit
After the setting of the applied voltage to the energy generation source 1 by 11 is completed, the charging is completed after a lapse of a predetermined time, and then the trigger control unit 10 sends a trigger pulse to the energy generation source 1 (step 105). As a result, the energy source 1 emits the energy beam EB with the variation of the pulse energy amount suppressed within (ΔP / P).

Then, the energy amount monitor unit 5 measures the oscillation energy amount by the monitor device 4, the calculator 6 will sequentially accumulating the amount of energy per pulse, and calculates the cumulative energy amount I ₀ (step 106). Then, in step 107, the calculator 6 determines whether or not the integrated energy amount I ₀ (actually measured value) satisfies the energy amount control accuracy A ₀ . That is,
It is determined whether or not the integrated energy amount I ₀ satisfies the following equation (11).
The sequence of two energy irradiations ends.

| 1− (I ₀ / S ₀ ) | ≦ A (11) On the other hand, if the above equation (11) is not satisfied, step 10
Advances to 8, wherein on the basis of the data before the pulse (V _1, P _1), and updates the parameters _{C 1 ~C 5, D 1 ~D} 3 from equation (6). In this embodiment, a sequence for updating a parameter for each pulse is employed. And the next step
Calculator 6 in 109, after calculating the applied voltage V ₂ second shot-th determines the pulse energy P _2, further (7) corresponding to the pulse energy P ₂ from the equation according to equation (10), a step Return to 105. The main control system 9 in step 105 based on the applied voltage V _2, provides an instruction signal to the operation similar to the applied voltage control unit 11 and the trigger control 10, further calculates a cumulative energy amount I ₀ by the computing unit 6 ( Steps
106), cumulative energy amount I ₀ is the step 107 (1
1) Judge whether the expression is satisfied. If not, the process proceeds to step 108 again, and steps 105 to 109 are repeatedly executed until the above expression (11) is satisfied.
When the expression (11) is satisfied, the energy irradiation operation ends.

Therefore, by repeatedly performing the above operation, even if the relationship between the applied voltage V and the oscillation energy amount P changes with time during the energy irradiation operation, the relational expression (formula (3)) expressing the change with time changes. Since it is appropriately updated according to the change, it is possible to always achieve good energy amount control accuracy.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a plan view showing a schematic configuration of an energy amount control device according to the present embodiment. Here, a pulse laser light source that emits pulsed light in the far ultraviolet region is used as the energy generation source 1, and a reticle A configuration applied to a stepper that transfers an R pattern onto a wafer W with a predetermined exposure amount is shown. In FIG. 4, the first
Members having the same functions and functions as those of the embodiment (FIG. 1) are denoted by the same reference numerals.

In FIG. 4, a trigger control unit 10, an applied voltage control unit 11
Sends a trigger pulse to the pulse laser light source 1 based on a command from the main control system 9 and an applied voltage corresponding to the energy amount of the pulse light to be irradiated next, as described in the first embodiment. is there. The pulse laser light source 1 has a band narrowing wavelength stabilizing mechanism composed of an etalon, a dispersing element, and the like at a part between two resonance mirrors disposed at both ends of a laser tube. As a laser light source. Further, by generating a high-voltage discharge between two electrodes provided in parallel along the optical axis of the laser light, far-ultraviolet light having a wavelength sensitive to the resist layer, for example, KrF excimer laser light (wavelength 248 nm).

Laser beam LB ₀ emitted from pulsed laser light source 1
Has a rectangular cross section corresponding to the arrangement shape of the two electrodes, that is, a rectangle whose beam cross section has an aspect ratio of about 1/2 to 1/5.
Therefore, the laser beam LB ₀ is incident on a beam expander 14 (beam cross-sectional shape conversion optical system) combining two sets (irregularities) of cylindrical lenses, and the beam expander 14 reduces the width of the laser beam LB ₀ in the width direction. Expand,
Beam cross section is emitted as a laser beam LB ₁ that has been converted into a substantially square shape.

The exit beam LB ₁ from the expander 14 enters the light reduction unit 15, where the beam light amount (energy) is 0%
It is attenuated continuously or stepwise between (complete transmission) and 100% (complete light blocking). The dimming control unit 12 is the dimming unit 15
To send a predetermined drive command to the dim ratio (or transmittance)
Is controlled. The extinction ratio (or transmittance) of the extinction unit 15 is determined by the number of pulses Nsp required to smooth an interference pattern generated on the reticle R or the wafer W, and the integrated light amount given to the wafer W. This is determined from the pulse number Nexp required for actual exposure, which is determined from the pulse number Ne required for control with the amount control accuracy, and the appropriate exposure amount.

Here, for example, assuming that the dimming rate of the dimming unit 15 is set to six discrete steps, the dimming rate is selected based on the pulse number Nexp and the appropriate exposure amount before the start of exposure, and at least 1 It is not changed to another value during the exposure of one shot. In other words, the dimming unit 15 always reduces the light amounts of all the pulse lights by a predetermined amount unless the exposure conditions for the wafer W (for example, an appropriate exposure amount per shot according to the sensitivity characteristics of the resist) change. The light amount is uniformly attenuated by the light rate, and a light amount adjusting mechanism having a relatively low response speed (light-changing rate switching speed) may be used.

As the light reducing unit 15 suitable for use in the present embodiment, for example, a method in which six types of mesh filters having different attenuation rates (transmittances) are attached to a turret plate and the turret plate is rotated is adopted. FIG. 5 shows an example of the structure of the rotating turret plate 16 and the six types of mesh filters 16a to 16f. The filter 16a is a mere opening (transparent) part and has an attenuation factor of 0% (that is, a transmittance of 100%). %). Each of the filters 16a to 16f is arranged at approximately six positions along a circle centered on the rotation axis of the rotary turret plate 16 at an interval of about 60 °, and one of the filters is a substantially square beam LB ₁ from the expander 2. Are arranged in the optical path.

FIG. 6 shows the relationship between the amount of rotation of the rotating turret plate 16 shown in FIG. 5 and the transmittance. Here, it is shown as a filter 16a is a rotation amount zero when positioned in the optical path of the beam LB _1, it rotates the rotary turret plate 16 counterclockwise in the drawing sheet of Figure 5. Sixth
In the figure, when the rotary turret plate 16 by about 60 ° (π / 3), the beam LB ₁ is dimmed at a predetermined rate. still,
When the rotation amount is 2π (360 ° or 0 °), the filter 16a is selected, and the transmittance becomes 100%.

Here, as the dimming element attached to the rotating turret plate 16, a dielectric mirror having a different transmittance may be used other than the mesh filter. Further, two sets of rotating turret plates 16 are provided so as to be relatively rotatable at a fixed interval, and for example, the transmittance of the dimming element of the first rotating turret plate is set to 100%, 90%, 80%, 70%, 60%. , 50%, and the transmittance of the dimming element of the second rotating turret plate is 100%, 40%, 30%, 20%.
If set to%, 10%, and 5%, a total of 36 transmittances can be realized by a combination of the two.

It is to be noted that a predetermined short aperture and a zoom lens system are combined as the dimming unit 15 to continuously dimm the light by changing the zoom ratio and the aperture diameter. A method of rotating a so-called etalon, which is held substantially in parallel at intervals, a method of relatively moving two phase gratings or light and dark gratings, or rotating a polarizing plate when linearly polarized laser light is used as exposure light. A system or the like may be adopted.

Returning to the description of FIG. 4, the substantially parallel beam LB ₁ ′ that has undergone a predetermined attenuation in the light reduction unit 15 enters an interference pattern reduction unit 17 that smoothes an interference pattern. The interference pattern reduction unit 17 has a vibrating mirror (galvanometer mirror, polygon mirror, etc.) that vibrates one-dimensionally (or two-dimensionally) by an actuator (piezo element, etc.), and the beam LB to the fly-eye lens 19 is provided for each pulse. By changing the ₁ 'angle of incidence, the interference pattern can be one-dimensional (or two-dimensional) on the reticle
It is moved and finally smoothed, in other words, the illuminance uniformity is improved.

Now, the beam LB ₁ ′ that has passed through the interference pattern reduction unit 17
Is turned into a vibrating beam that swings one-dimensionally (or two-dimensionally) at a minute angle, is then turned back by a mirror 18 and is incident on a fly-eye lens 19 as an optical integrator.
Therefore, the beam LB ₁ ′ incident on the fly-eye lens 19 is
The angle of incidence on the plane of incidence of the fly-eye lens 19 changes every moment. Here, the fly-eye lens 19 is formed by bundling a plurality of rod-shaped element lenses. The exit end of the fly-eye lens 19 has the same number of secondary light source images as the number of element lenses (here, each of the partial luminous fluxes of the beam LB ₁ ′). (Light spot).

FIG. 7 shows the relationship between the incident beam of the fly-eye lens 19 and the secondary light source image (spot light).
FIG. 2 is a schematic explanatory diagram according to the principle disclosed in Japanese Patent Application Publication No. H10-115,004.
Each rod lens 19a of the fly-eye lens 19 is a quadrangular prism made of quartz glass having convex spherical surfaces formed at both ends. When a beam LBb (parallel light beam) enters the fly-eye lens 19 in parallel with the optical axis AX, each rod lens 19a of the fly-eye lens 19
The spot light SPb is condensed at the exit end of the lens or at a position where it comes into the air by a predetermined amount from the exit end. Although this spot light SPb is shown for only one rod lens in FIG. 7,
Actually, the beam LBb is formed on all the emission sides of the rod lens to be irradiated. Moreover, each spot light SPb is focused on the beam LBb substantially at the center of the exit surface of the rod lens. On the other hand, when a parallel beam LBc inclined rightward with respect to the optical axis AX enters the fly-eye lens 19,
The light is condensed as spot light SPc on the left side of the exit surface of each rod lens 19a. Similarly, the parallel beam LBa inclined leftward with respect to the optical axis AX is condensed as spot light SPa on the right side of the exit surface of the rod lens 19a. Therefore, due to the one-dimensional vibration of the parallel beam LB ₁ ′ by the interference pattern reduction unit 13, all of the plurality of spot lights generated on the exit side of the fly-eye lens 19 are one-shot with respect to the fly-eye lens 19 (optical axis AX). In the same direction.

In this way, a plurality of beams LB ₂ forming each spot light formed on the exit side of the fly-eye lens 19 are transmitted through the beam splitter 2 as shown in FIG. 4, and are incident on the condenser lens CL. , On the reticle R. As a result, the reticle R is illuminated with a substantially uniform illuminance distribution, and the pattern of the reticle R is changed by the projection lens PL onto the wafer W (the irradiation object 3 in the first embodiment) mounted on a stage (not shown). Is transferred to the resist layer at a predetermined exposure amount. At this time, a plurality of spot lights formed at the exit end of the fly-eye lens 19 are re-imaged at least on the pupil (entrance pupil) Ep of the image (wafer) side telecentric projection lens PL, and a so-called Koehler illumination system is configured. You.

As described above, the interference pattern reduction unit 17 moves the interference fringes generated on the reticle surface or the wafer surface by a small amount by vibrating the beam incident on the fly-eye lens 19,
When the exposure is completed, the resulting bright and dark fringes transferred to the resist layer are smoothed to reduce the visibility of interference fringes. In the present embodiment, when smoothing the interference pattern, the laser light incident on the fly-eye lens 19 is vibrated. In addition to this, for example, a configuration in which the rotary diffuser is rotated in synchronization with the emission of the pulse light is used. Is also good.

Next, the beam LB ₂ split by the beam splitter ₂
Is collected on the light receiving surface of the light receiving element 4 'by the light collecting optical system 20. Light-receiving element 4 'is for outputting a photoelectric signal corresponding to the amount (light intensity) of each of the beam LB ₂ pulses correctly, composed of a PIN photodiode or the like having a sufficient sensitivity in the ultraviolet region. The photoelectric signal output from the light receiving element 4 'is input to a light quantity monitor 5', and is converted into an actual light quantity for each pulse by the light quantity monitor 5 '. Therefore, the light receiving element
4 ′ and the light amount monitoring unit 5 ′ constitute an energy amount measuring unit of the present invention, and the energy amount measured in this way is sent to the calculator 6, where the light amount for each pulse is sequentially integrated, The measured value (light amount) in the arithmetic unit 6 is used for controlling the exposure amount, updating the information on the relationship between the applied voltage of the pulse laser light source 1 and the oscillation energy amount, and for each shot of the trigger pulse oscillated from the trigger control unit 10. This is the basic data for oscillation control. Note that the relationship between the actual light amount of the laser beam irradiated onto the wafer W by the power meter and the sensitivity of the light receiving element 4 'is determined in advance for the light receiving element 4'. Is stored in Further, the light amount for each pulse may be sequentially integrated by the light amount monitoring unit 5 ′, and the integrated light amount and the light amount for each previous pulse may be output to the arithmetic unit 6.

The arithmetic unit 6 updates the information on the relationship between the applied voltage (or charging voltage) and the oscillation energy amount (or dose amount) according to the present invention, and applies an application corresponding to the pulse energy amount to be irradiated next. Means for determining a voltage, the role of which is as described in the first embodiment. However, in this embodiment, the interference pattern is smoothed (illuminance uniform).
Is different from the first embodiment. Therefore, the energy control logic in the arithmetic unit 6 in this embodiment is different from that in the first embodiment, and will be described later in detail.
Although the charging voltage measuring means is not shown in the present embodiment as in the first embodiment, the arithmetic unit 6 updates information on the relationship between the charging voltage and the oscillation energy amount instead of the applied voltage. Needless to say, such a configuration may be adopted.

The main control system 9 outputs the command of the applied voltage and the oscillation trigger pulse determined by the computing unit 6 to each of the applied voltage control 11 and the trigger control unit 10, and furthermore, the dimming degree and the interference pattern in accordance with various calculation results. A predetermined command signal relating to control is sent to each control unit to control the overall operation of the stepper. Further, it outputs the final integrated light amount (total exposure amount to the wafer W) to the input / output device 8 as necessary. I / O device 8
Is a man-machine
An interface that receives various parameters required for exposure from an operator and notifies the operator of the operation state of the stepper.

The memory 7 stores parameters (constants) and tables required for the exposure operation and various calculations input from the input / output device 8, or the sensitivity characteristics of the light receiving element 4 '. In particular, in this embodiment, while the beam LB ₁ ′ oscillates for a half cycle by the interference pattern reduction unit 17, the minimum number of pulses necessary for smoothing the interference pattern (Nvib described later)
Is stored. Here, the half cycle of the beam means the spot light is SPa → SPb in FIG.
→ To move in the order of SPc (or reverse), the beam is moved to LBa →
This corresponds to inclining the swing angle α ゜ in the order of LBb → LBc (or reversely). Note that the actual tilt amount of the oscillating mirror is α ゜ / 2 from the double angle theorem.

Now, the arithmetic unit 6 calculates the number of pulses Nsp required to smooth the interference pattern stored in the memory 7 in advance, and 1
Based on the pulse number Ne required to achieve the desired exposure amount control accuracy in the shot exposure and the data on the appropriate exposure amount S per shot according to the sensitivity characteristics of the resist, the dimming unit 15 is reduced. The light rate β and the average light amount per pulse (· β) described later are calculated. The arithmetic unit 6 calculates a target integrated light amount to be given to the wafer W when each pulse is irradiated with the average light amount value, and then calculates the target integrated light amount and the actual measurement amount transmitted from the light amount monitoring unit 5 ′. The difference D from the actual integrated light amount obtained by sequentially integrating the values (energy amounts) is calculated. Then, an applied voltage of the pulse laser light source 1 is calculated based on the difference D, and information on the applied voltage is output to the main control system 9.

In other words, the computing unit 6 calculates the light quantity of the pulse light to be irradiated next from the average light quantity value (· β) based on the difference D, and sends it to the main control system 9. Then, based on this correction value, the applied voltage control unit 11
In other words, the applied voltage is controlled, that is, the applied voltage is corrected by the amount corresponding to the above-mentioned correction value and applied to the pulse laser light source 1. Incidentally, an example of the relationship between the voltage applied to the pulse laser light source 1 and the light quantity (pulse energy) of the emission pulse is as shown in FIG.

Further, the main control system 9 outputs a drive signal to the interference pattern control unit 13 so that the pulse emission of the pulse laser light source 1 and the deflection angle of the beam by the interference pattern reduction unit 17 are synchronized. Note that this synchronization follows the output of a detector that monitors the beam deflection angle with high precision, and sends an oscillation start and stop signal to the trigger control unit 10 so as to trigger the pulse emission of the pulse laser light source 1. You may make it output.

Here, the dimming unit 15 described above is not only at the position shown in FIG. 4, but also between the pulse laser light source 1 and the expander 14, or between the cavity mirror inside the pulse laser light source 1. The same effect can be obtained even if it is inserted. Further, when the method of causing the beam to vibrate at a small angle by the interference pattern reducing unit 17 described above is not adopted, the beam may be inserted between the interference pattern reducing unit 17 and the fly-eye lens 19. However, in any case, the dimming unit 15 needs to be placed in a stage before the laser light enters the fly-eye lens 19.
Since light-reducing elements such as mesh filters often cause deterioration of illuminance uniformity in the beam cross section,
This is because the fly-eye lens 19 needs to solve this.

Next, the minimum number of pulses Nsp required for smoothing the interference pattern (uniform illuminance) will be described. For the smoothing of the interference pattern, see, for example, JP-A-1-257327.
Since it is disclosed in the official gazette, it will be briefly described here. In the above publication, when an optical integrator, particularly an illumination optical system having a fly-eye lens is employed, a plurality of pulsed lights are irradiated while moving an interference pattern formed on a reticle (or a wafer) within a certain range. Therefore, when performing the smoothing, the minimum number of pulses to be irradiated during the movement of the interference pattern by one pitch is limited to a predetermined value in advance, and the pulse light of the number equal to or more than the minimum number of pulses must be irradiated. It uses the principle that it must be.

Now, as shown also in FIG. 7, the interference pattern is generated when the spot lights generated by the rod lenses of the fly-eye lens 19 interfere with each other. At this time, a case where only the spot lights of two rod lenses adjacent to each other interfere with each other, or a case where three spot lights in the arrangement direction of the rod lenses interfere with each other may be used. What is necessary is just to consider a case where a number of spot lights interfere with each other.

Therefore, theoretically, the minimum number of pulses necessary for smoothing an excellent interference pattern is determined according to the number of spot lights that interfere with each other among the numbers in the arrangement direction of the rod lenses constituting the fly-eye lens 19. Nsp, and the minimum number of pulses Nvib to be irradiated during a half cycle of the beam swing by the vibrating mirror required for one pitch movement of the interference pattern (Nvib is Nvib ≧ Nvib)
Nsp) is also determined.

For example, when only two adjacent spot lights interfere with each other, the intensity distribution of the interference pattern is mathematically and theoretically a simple sine wave. In order to smooth this interference pattern, it is sufficient to irradiate two pulses, one pulse before and after shifting the phase difference between the two spot lights by π (movement of a half cycle of the interference pattern). . In general, when n spot lights interfere with each other, theoretically, the interference pattern is shifted by 1 / n period while being 1 / n.
Irradiation with pulses enables smoothing with a total of n pulses.

Here, considering the intensity distribution in one direction (for example, the Y direction) of the interference pattern generated on the reticle when one pulse is emitted, generally, bright stripes and dark stripes alternate with a predetermined pitch Yp in the Y direction. line up. However, the pitch Yp determined by the arrangement pitch of the rod lenses of the fly-eye lens, the wavelength of the laser beam, and the like depends on the configuration of the fly-eye lens, such as a two-stage structure.
In addition to the basic component, weak interference fringes whose intensity changes at a finer pitch may appear in a superimposed manner. Therefore, in practice, complete smoothing is rarely achieved under the above conditions, and the optimum value of the minimum pulse number Nsp required for smoothing the interference pattern needs to be determined by experiments or the like.

In the present embodiment, the angle change of the vibrating mirror (not shown) and the light emission pulse interval (frequency) are set based on the minimum pulse number Nsp obtained by experiments so as to satisfy the relationship of n · ΔY ≧ Yp. Then, an interference pattern is sequentially formed on the resist layer by a minute amount ΔY in the Y direction for each emission of one or more pulses.
By shifting by (ΔY <Yp), the interference pattern is smoothed (illuminance uniformity) at the time of completion of exposure, and a substantially constant illuminance distribution including a minute amount of ripple is obtained so as not to affect accuracy. It is to be.

Then, considering the conditions required for uniformity of illuminance, the following two conditions are given.

(1) Within a half cycle of the mirror oscillation (a period during which the beam swing angle changes from 0 ° to α °), pulse emission of a certain number Nsp or more is performed substantially uniformly.

Here, the pulse number Nsp is determined by the visibility of the interference pattern, and the larger the visibility, the larger the value of Nsp. Further, the pulse number Nsp is determined in advance by an experiment such as trial printing, and the numerical value differs between apparatuses having different optical systems. Therefore, when the pulse light emission of a number smaller than Nsp is almost uniformly distributed within a half cycle of the beam swing angle change (0 ° → α ゜), it is desirable in terms of uniform illuminance (illumination unevenness on the image plane). Within the precision of

(2) The average exposure energy per pulse at a predetermined angle of the vibrating mirror is calculated in the beam swing range (0 ° →
α ゜) must be substantially constant for any angle in the range.

The second condition is that the total number of pulses Nexp actually required for one-shot exposure is an integral multiple of the number of pulses Nvib in a half cycle of the beam oscillation, and that the first pulse light is subjected to mirror oscillation ( 0 ° to α ゜ / 2) (eg, beam LBa in FIG. 4)
Is achieved by emitting light at an angle of 0 °). When the pulse number Nexp is an integral multiple of the number of pulses in one cycle of the mirror oscillation (0 ° to α ゜ / 2), the first pulse light is transmitted to the mirror oscillation (0 ゜ to α ゜ / 2). The light emission may be started at an arbitrary angle in (3).

From the above, the above two conditions (1) and (2)
, The average exposure energy per pulse is adjusted to determine the optimal number of pulses, so that uniformity of illuminance and control of the amount of exposure can both be extremely efficiently achieved. Further, if not only the exposure energy but also the oscillation period (oscillation speed) of the oscillation mirror is changed, the number of exposure pulses is not increased more than necessary, which is advantageous in throughput.

The voltage applied to the pulse laser light source 1 is set to a value slightly smaller than the maximum applied voltage Vmax to the pulse laser light source 1 in consideration of a variation in exposure energy for each oscillation pulse. In one-shot exposure, after the first pulse light is emitted under the above set value, the main control system 9 determines the applied voltage for each of the second and subsequent pulses by the computing unit 6.
Are sequentially controlled to the voltage values calculated by. Therefore, an exposure energy control range by controlling the applied voltage of the pulse laser light source 1 will be described next. The average exposure energy per pulse (under the dimming rate of the dimming unit 15 is 1), the variation between the pulses of the exposure energy is Δ, and the pulse emission is performed N times in one shot exposure. Then, the variation of the actual integrated light amount I with respect to the target integrated light amount · N (S = · N at the appropriate exposure amount S) is expressed by the following equation (12).

As is apparent from the above equation (12), the control ratio of the light amount by the applied voltage control is 0 <Δ / <1, and パ ル ス 1 ± (Δ /) / (1-
Δ /)｝. Therefore, in order to prevent the maximum value {1 / (1−Δ /)} of the control ratio from exceeding the maximum value of the exposure energy control range, the average exposure energy control value set before the exposure must be adjusted. , The maximum value of the control range may be set to (1-Δ /) times or less.

In practice, the average exposure energy is set to be less than (1−Δ /) times the maximum output of the pulse laser light source 1,
The applied voltage (discharge voltage between electrodes) to the pulse laser light source 1 that can obtain the desired exposure energy may be set based on the relationship shown in FIG. For example, in the case of an excimer laser, since (Δ /) = about 10%, the exposure energy at the maximum applied voltage of the pulse laser light source 1 is set to 10 mJ / c.
Assuming m ² , the applied voltage may be set so that the exposure energy is 9 mJ / cm ² or less. In actuality, the exposure energy is set to, for example, 5 m in consideration of the phenomenon of a decrease in laser density (a decrease in output due to deterioration of the mixed gas) and the life of optical components.
It is desirable to set the applied voltage so as to be J / cm ² or less.

In the present embodiment, since the extinction rate of the extinction section 15 is changed according to the exposure conditions (the type of the resist, the appropriate exposure amount, etc.) on the wafer W, the exposure energy of the second and subsequent pulsed light is Fine adjustment is performed only to correct an error in the integrated light amount due to variation between pulses. Therefore, it is not necessary to greatly change the inter-electrode discharge voltage in the pulse laser light source 1, and the dynamic lens of the applied voltage control unit 11 can be small. For this reason, the relationship between the applied voltage and the exposure energy in one-shot exposure only needs to use a very small part of the graph shown in FIG. 2, and the relationship can be sufficiently approximated by a linear expression. .

Next, a brief description will be given of the pulse number Ne required to achieve a desired exposure amount control accuracy A (A = 1−I / · N) in one-shot exposure. Since the exposure amount control in the present embodiment adjusts the exposure energy for each pulse and makes the actual integrated light amount I substantially equal to the target integrated light amount / N, the error of the final integrated light amount is The exposure energy of the final pulse light becomes uneven. Therefore, in order to achieve the exposure control accuracy, the variation in the exposure energy of the final pulse light must be within the tolerance of the exposure control accuracy. That is, the exposure energy must be set to a small value, and the number of pulses N (N = S /) required for one-shot exposure must be a relatively large number. From this, in the above equation (12), (Δ
/) Since ^N can be regarded as zero, dividing each side by .N and rearranging it, the exposure amount control accuracy A becomes It is expressed as Here, in equation (13), the exposure amount control accuracy A
Is the maximum permissible error, ie , The number N of pulses required to achieve the exposure amount control accuracy becomes the smallest. Thus, the pulse number Ne is expressed by the following equation (15).

Therefore, at least the number of pulses represented by the above equation (15)
If exposure is performed with pulse light of a number equal to or greater than Ne, the final integrated light amount I is ± A (for example, 1%
In the case of A, the control accuracy of A = 0.01) is guaranteed.

Next, a method of determining the number Nexp of exposure pulses for one shot will be described. Generally, the number of exposure pulses Nexp is Nexp =
iNT (S /). Note that iNT (ω) indicates that the real value ω is rounded up to the nearest whole number and converted to an integer value.

Now, the pulse light oscillated from the pulse laser light source 1 is uniformly attenuated by the dimming unit 15 at a predetermined dimming rate β (0 ≦ β ≦ 1) and is irradiated on the reticle R. For this reason, the number Nexp of exposure pulses is required to satisfy the following conditional expression (16).

In order to achieve the exposure amount control accuracy A described above, the following expression (17) must also be satisfied.

Nexp ≧ Ne (17) Further, in order to smooth the interference pattern, the number Nexp of exposure pulses must be an integral multiple of the number Nvib of pulses in a half cycle of the vibrating mirror. Therefore, the number of exposure pulses Nexp
Is represented by the following equation (18).

Nexp = m · Nvib ≧ m · Nsp (m: m ≧ 1 integer) (18) Accordingly, the extinction ratio β of the extinction unit 15 is given by the following equations (15) to (17). It is expressed as

Further, the integer m is represented by the following equation (20) from the equations (15), (17), and (18).

Further, since the extinction ratio β is 1 or less, (16), (1
From equation (8), it is expressed as follows.

From the above, in this embodiment, first, (1
9) The dimming rate of the dimming unit 15 is determined so as to satisfy the expression, that is, the filter of the rotating turret plate 16 is selected. Next, it is checked whether the pulse number Nexp calculated from the expression (16) under the extinction ratio of the selected filter satisfies the expressions (17) and (18). If not, select a filter that satisfies equation (19) and has a smaller dimming rate.
The number of exposure pulses Nexp is set to satisfy the expressions (17) and (18). When the number Nexp of exposure pulses is determined in this way, m and Nvib may be determined so as to simultaneously satisfy the expressions (20) and (21).

As an example, assuming that the variation Δ / between pulses of the average exposure energy is 10% (Δ / = 0.1) and the exposure amount control accuracy A is 1% (A = 0.01), the number of pulses is obtained from the equation (15).
Ne has 12 pulses. On the other hand, when the dimming rate β of the dimming unit 15 is 1, the average exposure energy is ² mJ / cm ² , the appropriate exposure S is 80 mJ / cm ² , and the number of pulses Nsp required for smoothing the interference pattern is 50 pulses. From equation (16), the number of exposure pulses N
Although exp becomes 40 pulses, this pulse number Nexp does not satisfy the expression (18). Therefore, the dimming rate of the dimming unit 15 is set to be smaller than 1, and the dimming rate, that is, the number Nexp of the exposure pulses calculated from the equation (16) under the average exposure energy · β Try to meet.

Here, when the extinction ratio β of the extinction unit 15 can be set continuously, since Ne = 12 and Nsp = 50 pulses, (2
0), m, Nvib are set based on equations (21). At this time,
The combination of (m, Nvib) is, for example, (1,50), (1,60),
(2,100) etc., but here, the number of exposure pulses Nexp (Nexp = mNvi
In order to minimize b), m = 1 and Nvib = 50 are set, and the number of exposure pulses Nexp is set to 50. If exposure is performed with Nexp = 50, optimization of the exposure amount and smoothing of the interference pattern can be performed with the minimum number of pulses Nexp. As a result,
From equation (16), the dimming rate β of the dimming unit 15 is set to 0.80. From Δ / = ± 10%, Δ is ± 0.2mJ /
cm ^2, and the variation Δ · β of the average light amount value / β becomes ± 0.160 mJ / cm ² . Therefore, the variation of the average light amount value of the final pulse light, that is, the error of the final integrated exposure amount is ± 0.
Since it can be regarded as about 160 mJ / cm ² , it can be seen that the exposure amount control accuracy (1%) is sufficiently achieved.

On the other hand, when the setting of the dimming rate β of the dimming unit 15 is discontinuous (when the dimming unit 15 is a rotating turret plate or the like), (1)
9) A mesh filter of the rotating turret plate 16 that satisfies the expression is selected, and the extinction ratio of this filter (for example, β = 0.
5) pulse number Nex calculated from equation (16)
Check whether p satisfies equation (18). Here, in order to minimize the above-mentioned Nexp, a filter that satisfies the expression (19) is selected from the filter having the largest dimming rate. In the case of β = 0.50 (ie, β = 1 mJ / cm ² ), Nexp = 80 pulses, which satisfies the expressions (17) and (18). If the number of pulses Nexp is determined in this manner, since Nexp = 80, it is only necessary to determine m and Nvib that simultaneously satisfy the expressions (20) and (21).
= 1, Nvib = 80.

Note that, as is apparent from the above, when the setting of the dimming rate of the dimming unit 15 is discontinuous, the dimming rate cannot always be set to the optimum value obtained from the calculation. , The number of pulses Nexp becomes large, which may be disadvantageous in throughput. For this reason, the dimming unit 15 can continuously set the dimming rate, or can set the attenuation rate (transmittance) finely even if it is discontinuous (for example, two rotations). It is desirable to use a combination of a turret plate).

Next, a method of updating information relating to the relationship between the applied voltage and the oscillation energy amount, which is central in the present embodiment, will be described in detail. As described above, in this embodiment, since the dynamic range of the exposure energy control by the applied voltage control is small, a part of the relationship shown in FIG. 2 is used. Therefore, the relationship between the applied voltage and the amount of oscillation energy can be sufficiently approximated by a linear function. Therefore, when a function is applied to the relationship between the applied voltage and the amount of oscillation energy, it is sufficient to proceed with the linear function. Therefore, the model function in the present embodiment is expressed as follows.

P = s + tV (22) where s and t are parameters obtained by the least squares method. Further, in the present embodiment, the evaluation function E is represented by the following equation in consideration of the weight γ _i given to the data (V _i , P _i ).

Now, the unknowns s, t that minimize the evaluation function E are given by the least squares theory. By solving the following simultaneous equations, the following equation can be obtained.

However, Here, just as in the first embodiment, the weight γ _i for the data is set as in equation (4), and each element of the matrix on the right side of equation (24) is expressed as in the following equation.

At this time, as the information on the relationship between the applied voltage and the oscillation energy amount, each of the above-described elements, that is, the parameters G _{1 to} G ₃ ,
H ₁ and H ₂ are stored in the memory 7. Then, new data (V
_i , P _i ), that is, when the latest data (V ₁ , P ₁ ) is obtained,
The arithmetic unit 6 fetches the parameters G _{1 to} G ₃ , H ₁ , and H ₂ from the memory 7, and except for the constant G ₁ (G ₁ = 1 / (1−ε ² ))
G ₂ and G ₃ and H ₁ and H ₂ are updated using the recurrence formula shown below. As a result, by applying the recurrence formula, the operation time required for updating the information on the relationship between the applied voltage V and the oscillation energy amount P can be shortened, and the arithmetic unit 6 newly stores the updated information in the memory 7. Will do.

Therefore, G ₂ , G ₃ and H ₁ , H ₂ are appropriately updated by the above equation (26) at the unit pulse number or at regular time intervals, and further (2
4) If the unknowns s and t are obtained by calculating the equation, the applied voltage V
The relational expression (Expression (22)) between the pulse energy and the oscillation energy amount P is updated, and the applied voltage V corresponding to the oscillation energy amount P of the pulse light to be irradiated next can be obtained by Expression (22).

Next, the operation of this embodiment will be described with reference to FIG. FIG. 8 is a schematic flowchart showing an example of the operation of the present embodiment. First, the computing unit 6 in step 200, the parameters G ₁ ~G ₃ stored in the memory 7,
Determine whether or not to initialize H ₁ and H ₂ , and set parameter G
_{When 1 to} G ₃ , H ₁ and H ₂ are sufficiently reliable, the process proceeds to step 203. On the other hand, when initialization is necessary, for example, when the pulse laser light source 1 is started or its oscillation is stopped for a long time, or immediately after the gas exchange of the active medium in the chamber is performed, the process proceeds to step 201. , The applied voltage V is changed in several ways within the range to be used (the range where the relational expression (22) can be sufficiently approximated by a linear function), and the light amount of each pulse oscillated under each voltage value is monitored. Take in from part 5 '. Thereafter, the data (V _i, P _i) calculator 6 is calculated in step 201 in step 202 based on the parameters G ₁ ~G ₃ from above (26), and calculates the H _1, H _2,
It is stored in the memory 7.

In the next step 203, the arithmetic unit 6 sets the input / output device 8
From the memory 7, the exposure control accuracy A from the memory 7 and the variation (Δ /
), The maximum applied voltage Vmax, and the number of pulses Nsp required for smoothing the interference pattern. Of course, the variation (Δ /) between pulses of the average exposure energy may be a value obtained from the data (V _i , P _i ) in step 201 as in the first embodiment. Next, the arithmetic unit 6 performs step 203
Based on each data captured in, the extinction rate β of the extinction section 15
(Average light value β), that is, the number of exposure pulses Nexp under the dimming rate of the filter of the rotating turret plate 16 and the selected filter, the number of pulses in the half cycle of the oscillating mirror
Nvib and an integer m are calculated (step 204). continue,
In step 205, the rotary turret plate 16 is rotated to set the dimming rate of the dimming unit 15 to β, and in step 206, the applied voltage V for obtaining the average exposure energy is calculated from the equation (22). Here, the average exposure energy is (1-Δ /) of the exposure energy max (maximum value) oscillated from the pulse laser light source 1 under the maximum applied voltage Vmax.
) It is desirable to set it to twice or less.

In the next step 207, the pulse counter n and the integrated light amount I are set to Nexp and zero, respectively. In the following step 208, the main control system 9 sets the pulse counter n
Is determined to be zero, and if not, the flow proceeds to the next step 209. Then, in step 209, the applied voltage control unit
After setting the applied voltage of the pulse laser light source 1 according to 11,
Pulse laser light source 1 from trigger controller 10
To emit one pulse. In the following step 210, a value a corresponding to the actual light amount of the pulse light oscillated by the light receiving element 4 'is detected and sent to the computing unit 6 via the light amount monitoring unit 5'. Next, in step 211, the arithmetic unit 6
Calculates the integrated light amount I and sets the integrated light amount to I = I +
and set the pulse counter to (Nexp-1)
And

Next, at step 212, the target integrated light amount to be given by the average light amount value / β determined at the previous step 204 according to the equation (27), the target integrated light amount and the actual integrated light amount I obtained by the arithmetic unit 6, Is obtained.

D = (Nexp−n) ·· β-I (27) Subsequently, in step 213, based on the difference D,
Next, the light amount ′ of the pulse light to be irradiated is obtained by correcting the average light amount · β determined in step 204 by equation (28).

In the next step 214, the arithmetic unit 6 determines the value of the previous pulse, that is, the applied voltage V applied to the pulse laser light source 1 in step 209 and the light amount a for one pulse detected in step 210. The parameters G _{1 to} G ₃ , H ₁ and H ₂ are updated from the above equation (26) and stored in the memory 7.
Then, in the next step 215, the arithmetic unit 6 calculates (22)
The applied voltage corresponding to the light amount ′ is calculated by the equation, and the process returns to step 208. In this step 208, it is determined whether or not the pulse counter n is zero, as in the operation described above. If not zero, go to step 209,
After performing the same operation as described above at 215, the process returns to step 208 again, and repeats steps 209 to 215 until the pulse counter n becomes zero. When the pulse counter n becomes zero, the exposure operation ends. .

Next, the state of exposure amount control in the apparatus according to the present embodiment will be described with reference to FIG. FIG. 9 is a graph showing the relationship between the number of pulses and the integrated exposure amount when exposing one shot, and here, a case where the exposure is completed by eight pulses is shown. For simplicity of explanation, it is assumed that the dimming rate β of the dimming unit 15 is set to 1.

In FIG. 9, the straight line indicated by the two-dot chain line
The target value of the integrated exposure amount to be given by the pulse light of the average light amount value / β determined in 4 is shown. Therefore,
In the present invention, the light amount is adjusted for each of the second and subsequent pulses so that the exposure amount control is performed according to the target value.

Now, the first pulse light is emitted with a target of an exposure amount of ₁ , and the actually detected exposure amount after the emission is
'When were, pulsed light of the second shot th target exposure amount 2 ₁ and _{1' 1} the difference between - so that light emission is set to (2 _{1 1} ') = ₂ becomes the light amount is performed. At this time, the applied voltage controller 11 only needs to apply an applied voltage corresponding to the light amount ₂ to the pulse laser light source 1. Similarly, 'When a was the third shot th pulsed light (3 ₁ - _1' - measured value of the second shot th pulse light amount _{2 2} ') = is set to ₃ comprising light amount emission line Will be

Therefore, by repeating the above operation, the exposure is completed at the eighth pulse in a state where the displacement of the two-dot chain line from the target line is small. At this time, it is clear that the final exposure amount control accuracy (variation of the actually measured value with respect to the appropriate exposure amount) is a light amount error (variation) of the eighth pulse light.

As described above, in the second embodiment of the present invention, when one shot is exposed with a plurality of pulsed lights, the target value of the integrated exposure amount up to the (i + 1) -th shot and the past value (up to the i-th shot) are obtained. Based on the difference from the integrated exposure amount, the (i +
1) The light quantity of the first pulse light was set. However, if there is any tendency in the variation method for each pulse, the ratio between the target value for each unit pulse and the actually measured value for each unit pulse is averaged over a plurality of past pulses, and the target value is calculated based on this ratio. A new target value may be set by dividing by the average value.

Further, in the second embodiment, the case where the pulse energy oscillated from the exposure illumination light source is a coherent laser beam has been described. However, the case where the light source of the exposure apparatus emits incoherent pulse light, For example, when emitting pulse energy other than light such as an electron beam, there is no need to consider reduction (smoothing) of interference pulses. Therefore, the minimum number of pulses (the number of pulses necessary to control the variation of the actual integrated exposure amount given to the wafer W by the irradiation of the plurality of pulse lights with the desired exposure amount control accuracy with respect to the target appropriate exposure amount) (Corresponding to the pulse number Ne in this embodiment) is determined from the fluctuation range of the pulse energy per pulse and the exposure amount control accuracy, and the target value of the pulse energy is determined for each pulse based on the pulse number and the optimal exposure amount. Should be set. That is, the error of the final integrated exposure amount with respect to the appropriate exposure amount is determined by the light amount error of the final pulse light, so that the variation of the final pulse falls within the allowable error of the exposure amount control accuracy (15). )), The number of pulses is determined, and the average amount of energy per pulse is set according to the expression (16).

Further, in the exposure apparatus of the above embodiment (FIG. 4), the applied voltage control for the pulse laser light source 1 is effective (necessary).
An important operation is wafer exposure and data collection for obtaining information on the relationship between the applied voltage and the exposure energy (step 201 in FIG. 8). Normally, the oscillation of the pulse laser light source 1 in the exposure apparatus is, for example, a detection reference position (mark detection center position) of an off-axis type alignment system that is provided separately from the projection lens PL and exclusively detects only alignment marks on the wafer W. It is also required when measuring the distance between the projection position (exposure position) of the projection image of the reticle R, that is, the so-called baseline. Here, the operation of measuring the baseline in an exposure apparatus using a pulse laser as a light source is disclosed in, for example, JP-A-64-10105, and the description thereof is omitted. However, a plurality of reflecting members (or optical fibers) are used. The illumination light transmitted from the pulse laser light source illuminates the reference mark provided on the wafer stage from below (inside the wafer stage), thereby projecting the alignment mark of the reticle R and the reference mark on the wafer stage. Then, the position of the wafer stage when is matched is detected.
Further, the position of the wafer stage when the mark detection center position matches the reference mark on the wafer stage is obtained using an alignment system, and the interval between these two points is used as a baseline. Therefore, it is not always necessary to control the applied voltage to the pulse laser light source 1 at the time of the baseline measurement as described above. Therefore, the oscillation mode of the pulse laser light source 1 can be switched between the applied voltage control mode and the constant energy amount mode (or the constant applied voltage mode) in accordance with the operation mode of the exposure apparatus, thereby performing wafer exposure and data collection in step 201. It is desirable to use the constant energy mode in operations other than the above.

As described above, in the first and second embodiments of the present invention, the information on the relationship between the applied voltage (or charging voltage) and the amount of oscillation energy (or dose) is described in (5) or (25).
Although expressed as a matrix element indicated by the formula, each element, i.e. the parameter _{C 1 ~C 5, D 1 ~D} 3, or in place of _{G 1 ~G 3, H 1,} H 2,
For example, the ratio of unknowns a ′ to c ′ or s ′, t ′ at the time of updating (step 108 or 214) with respect to unknowns a to c or s, t at the time of initialization (step 102 or 202) of the above relation is calculated as above. Information may be used, and the correction rate of the applied voltage required to obtain a predetermined pulse energy with respect to the applied voltage at the time of the initialization of the above relationship may be provided as a function of the pulse energy, and this function may be updated as appropriate. Absent.

Further, in the first and second embodiments of the present invention, a case has been described in which the information on the relationship between the applied voltage (or charging voltage) and the amount of oscillation energy (or dose) is updated for each pulse. High frequency and 1
If the operation time for each pulse cannot be sufficiently obtained, the information may be updated every unit number of pulses (for example, every five pulses) or every certain time. On this occasion,
It is desirable to set the update interval of the above information to a time sufficiently shorter than the temporal change of the relationship between the two. In the case of the above method, a method (thinning method) that uses only data for each unit pulse number or for every fixed time and does not use other data is expected to be the least computational and effective.

〔The invention's effect〕

As described above, in the present invention, the applied voltage (or charging voltage) and the oscillation energy amount (or dose amount) are appropriately captured for each unit number of pulses or for each unit time,
It was decided to update the relational expression between them by calculation. Therefore, the above relational expression is updated successively according to the temporal change in the relation between the applied voltage and the oscillation energy amount, so that good energy amount control is always possible.

Even when the energy generation source is a pulse laser and the partial gas exchange of the laser or the like is performed along with the exposure operation, the temporal change in the relationship between the applied voltage and the oscillation energy (that is, the mixed gas in the chamber). The above-mentioned relational expression can be updated in accordance with the following equation.
In particular, the exposure apparatus is advantageous in that the final interference pattern is almost completely smoothed (uniformity of illuminance), and even if the output of the pulse laser light source is reduced, the exposure amount can be more accurately compared to the conventional method. It is possible to perform one-shot exposure with the minimum necessary number of pulses while optimizing and smoothing the interference pattern, thereby improving productivity.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an energy amount control device according to a first embodiment of the present invention, and FIG. 2 is a diagram showing an applied voltage at an energy generating source and an output (pulse energy) under the applied voltage. FIG. 3 is a flowchart showing an example of the operation of the energy control apparatus according to the first embodiment shown in FIG. 1, and FIG. 4 is a second embodiment of the present invention. FIG. 5 is a plan view showing a schematic configuration of a stepper provided with an energy amount control device according to an example, FIG. 5 is a configuration diagram showing an example of a rotating turret plate suitable for application to a dimming unit, and FIG. FIG. 7 shows the relationship between the amount of rotation of the dimming element and the transmittance when dimming is performed by the rotating turret plate shown in FIG. 7. FIG. 7 shows a beam incident on an optical integrator (fly-eye lens) and its secondary light source With the image (spot light) FIG. 8 is a diagram schematically showing the relationship, FIG. 8 is a flowchart showing an example of the operation of the energy amount control according to the second embodiment shown in FIG. 4, and FIG. 9 is the second embodiment shown in FIG. 9 is a graph showing a state of exposure amount control according to an example. [Description of Signs of Main Parts] 1 ... pulse oscillation type energy generation source, 5 ... energy amount monitor unit, 5 '... light amount monitor unit, 6 ... calculator, 7
…… Memory, 8 …… I / O device, 9 …… Main control system, 10…
... trigger control unit, 11 ... applied voltage control unit, 12 ... dimming control unit, 13 ... interference pattern control unit, 15 ... dimming unit, 16 ...
... Rotating turret plate, 17 ... Interference pattern reduction unit, 19 ...
… Fly eye lens, R… Reticle, PL… Projection lens, Ep… Entrance pupil, W… Wafer.

Claims (12)

(57) [Claims] 1. An energy source for emitting pulse energy with energy fluctuation within a predetermined range every time oscillation occurs, and an energy amount of the pulse energy is controlled by adjusting a voltage applied to the energy source. A storage unit configured to store information on a relationship between an applied voltage to the energy generation source and an energy amount of pulse energy emitted from the energy generation source under the applied voltage; Energy amount measuring means for detecting an energy amount of pulse energy actually ejected; for each predetermined unit number of pulses, or for each unit time, an applied voltage applied to the energy generation source; Stored in the storage means based on the detected energy amount. Calculating means for updating the information, and determining means for determining, based on the information updated by the calculating means, a voltage to be applied to the energy source corresponding to the energy amount of pulse energy to be emitted next. An energy control device, comprising: 2. The information according to claim 1, wherein said information stored in said storage means is obtained by oscillating said pulse energy while changing said applied voltage and detecting the amount of energy. Energy amount control device. 3. The information processing apparatus according to claim 1, wherein the calculating means updates the information by assigning a weight to each of the plurality of energy amounts detected by the energy amount measuring means.
Item 3. The energy amount control device according to Item 2. 4. The energy amount control according to claim 3, wherein the weight of the latest energy amount detected by said energy amount measuring means is made the heaviest, and the weight is lightened as it becomes older. apparatus. 5. An energy source for emitting pulse energy with energy fluctuation within a predetermined range every time oscillation occurs, and controlling an energy amount of the pulse energy by adjusting a voltage applied to the energy source. A storage unit for storing information relating to a relationship between a charging voltage at the time of energy oscillation in the energy generation source and an energy amount of pulse energy emitted from the energy generation source under the charging voltage; A charging voltage measuring unit for detecting a charging voltage of an energy generating source; an energy amount measuring unit for detecting an energy amount of pulse energy actually emitted from the energy generating source; for each predetermined number of unit pulses or for each unit time The measurement of the charging voltage measuring means and the energy amount measuring means Calculating means for updating the information stored in the storage means based on the result; and the energy source corresponding to the energy amount of the pulse energy to be emitted next based on the information updated by the calculating means And a determining means for determining a voltage applied to the energy control apparatus. 6. The energy amount control device according to claim 1, wherein the energy generation source oscillates excimer laser light. 7. An illumination system for irradiating a first object with the energy control device according to claim 1, wherein the pulse energy controlled by the energy control device is applied to a first object. An exposure apparatus, comprising: irradiating the first object with the pulse energy via the illumination system to transfer a pattern formed on the first object onto a second object. 8. A lighting system comprising: a first adjusting means for controlling a voltage applied to the energy source; and a second adjusting means provided in the illumination system separately from the first adjusting means. The exposure apparatus according to claim 7, wherein an energy amount of the pulse energy on the second object is adjusted by adjusting means. 9. An exposure control means for controlling an integrated energy amount of a plurality of pulse energies for irradiating a predetermined point on the second object to a predetermined value according to a sensitivity characteristic of the second object. 9. The exposure apparatus according to claim 8, wherein the means controls the second adjusting means based on an average energy amount of the plurality of pulse energies determined from information on the sensitivity characteristic. 10. The apparatus according to claim 9, wherein the second adjusting means changes the attenuation rate or the transmittance of the pulse energy in the illumination system stepwise or continuously.
Exposure apparatus according to Item. 11. The exposure control means controls the first adjustment means based on the determined applied voltage while irradiating the pulse energy onto the second object. Item 10. The exposure apparatus according to Item 9 or 10. 12. The exposure control means calculates an integrated energy amount of the pulse energy on the second object based on an output of the measuring means, and irradiates next in accordance with the integrated energy amount. 12. The exposure apparatus according to claim 11, wherein an energy amount of the pulse energy is determined.