JP2017156720A - Exposure apparatus and article manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology that is advantageous in terms of running cost for reducing the fluctuation in exposure dose.SOLUTION: There is provided an exposure apparatus that performs scanning exposure of a substrate using pulsed light supplied from a light source unit. The exposure apparatus includes a measurement unit that measures the energy of the pulsed light and a control unit that determines the number of pulsed light irradiated to the substrate while the substrate moves by a unit length in the scanning direction. The control unit determines the number of pulsed lights on the basis of the fluctuation amount in energy.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an exposure apparatus and an article manufacturing method.

  In a lithography process, which is a manufacturing process of a semiconductor device, a liquid crystal display device, etc., an exposure apparatus has a photosensitive substrate (resist material layer formed on the surface via an original plate (also called a reticle or a mask) and a projection optical system. Wafer, glass plate, etc.) are exposed.

  When performing scanning exposure with an exposure apparatus that uses an excimer laser light source, the target exposure amount (target integrated exposure amount) is adjusted by adjusting the scanning speed of the substrate, the oscillation frequency of the laser beam, and the energy per pulse of the laser beam. ) To expose the substrate.

  Further, it is known that when the substrate is exposed with pulsed light having a trapezoidal intensity distribution in the scanning direction, the exposure amount can vary depending on the position in the exposure region depending on the intensity distribution.

  Patent Document 1 describes that each time the intensity distribution of pulsed light is changed, the number of pulsed light applied to one point in the exposure region is selected so that the variation in exposure amount is minimized. Yes. Further, Patent Document 2 describes that the intensity distribution of pulsed light is devised so that the variation in exposure amount is reduced.

  In order to reduce the fluctuation of the exposure amount, it is known to generate (oscillate) the pulsed light under the condition that the variation in the energy of the pulsed light becomes small (Patent Document 3 and Patent Document 4).

JP 2010-021211 A JP 2000-036456 A JP 2004-022916 A JP 2011-091416 A

  Excimer laser light sources and exposure apparatuses are configured with consumable modules that need to be replaced when the number of pulsed light or the accumulated (cumulative) amount of energy exceeds a predetermined amount. In recent years, the number of pulsed light per unit period (annual) has increased with the improvement of the production capacity of the exposure apparatus, so that the replacement cycle of the consumable module tends to be shortened. That is, the running cost tends to increase.

  An object of the present invention is to provide a technique advantageous in terms of running cost for reducing fluctuations in exposure amount.

  According to one aspect of the present invention, there is provided an exposure apparatus that scans and exposes a substrate using pulsed light supplied from a light source unit, the measuring unit that measures the energy of the pulsed light, and the substrate in a scanning direction. A control unit that determines the number of the pulsed light irradiated to the substrate during the length movement, and the control unit determines the number based on the amount of variation in energy. An exposure apparatus is provided.

  According to the present invention, for example, it is possible to provide a technique that is advantageous in terms of running cost for reducing fluctuations in exposure amount.

The figure showing the relationship between the number of irradiation pulses and exposure nonuniformity. The figure explaining definite unevenness. The figure explaining the exposure nonuniformity which considered the dispersion | variation in the energy of pulsed light. The figure explaining stochastic unevenness. 1 is a schematic block diagram of an exposure apparatus in an embodiment. The figure which shows the relationship between the number of received light pulses and exposure nonuniformity when the variation amount of energy is changed with respect to specific intensity distribution. The figure which shows the structural example of the coefficient table in embodiment. The figure which shows another structural example of the coefficient table in embodiment. The figure which shows another structural example of the coefficient table in embodiment. The figure explaining the calculation method of the minimum irradiation pulse number in embodiment. The figure explaining that exposure nonuniformity changes with the position of a X direction. The figure explaining that exposure nonuniformity changes with the dispersion | variation states of the energy of pulsed light.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment, It shows only the specific example advantageous for implementation of this invention. Moreover, not all combinations of features described in the following embodiments are indispensable for solving the problems of the present invention.

<First Embodiment>
Hereinafter, an exposure apparatus using a pulse discharge excitation gas laser such as an excimer laser for the light source will be described. As described above, when the substrate is exposed with pulsed light having a trapezoidal intensity distribution in the scanning direction, the exposure amount may vary depending on the position in the exposure region (exposure unevenness) depending on the intensity distribution. Further, the laser oscillation by the pulse discharge excitation gas laser is pulse oscillation, and here, there is a variation in energy of the pulsed light. This variation in the energy of the pulsed light also causes exposure unevenness. The variation in energy of pulsed light is generally increased due to aging of the internal module of the laser.

  FIG. 1 shows the relationship between the number of irradiation pulses and the amount of exposure fluctuation (exposure unevenness). Here, the number of irradiation pulses means the number of pulsed light irradiated on the substrate while the substrate moves by a unit length in the scanning direction. According to FIG. 1, the exposure unevenness decreases as the number of irradiation pulses increases as a whole, and there is a local number of irradiation pulses that minimizes the exposure unevenness.

  Conventionally, the following proposals have been made as a method for uniformly irradiating the exposed area of the substrate. One is a method of performing exposure under the condition of the number of irradiation pulses that minimizes the exposure unevenness generated depending on the intensity distribution of the pulsed light, or changing the intensity distribution shape so that the exposure unevenness is reduced. The other is a method of performing exposure under laser oscillation conditions in which variations in energy of pulsed light are reduced.

  Although such proposals have been made individually, the influence of the component due to the intensity distribution of the pulsed light and the component due to the variation in the energy of the pulsed light on the exposure unevenness is not independent. That is, the exposure unevenness is not only dependent on the shape of the intensity distribution of the pulsed light, but is also affected by the amount of variation in the energy of the pulsed light.

  This will be described with reference to FIGS. FIG. 2 shows a schematic diagram (left diagram) of scanning exposure when there is no variation in the energy of pulsed light, and the relationship between exposure unevenness and the number of irradiation pulses (right diagram) at that time. Since there is no variation in the energy of the pulsed light, the intensity (height) of the trapezoidal distribution is the same (1.0) for all pulses, and the exposure unevenness that occurs at this time is determined only by the shape of the intensity distribution of the pulsed light. The Hereinafter, the exposure unevenness determined by only the intensity distribution shape without variation in the energy of the pulsed light is referred to as “deterministic unevenness”.

  FIG. 3 is a schematic diagram (lower left) of the light intensity of each pulse when the energy variation of 1% pulsed light exists (upper left) and the intensity distribution shape of the pulsed light at each position in the scanning direction during scanning exposure. The figure shows the relationship between the exposure unevenness and the number of irradiation pulses (right figure). The intensity (height) of the trapezoidal distribution varies in the range of 0.99 to 1.01, and the exposure unevenness that occurs at this time is determined by two factors: the intensity distribution shape and the amount of variation in the energy of the pulsed light. Hereinafter, the exposure unevenness determined by the intensity distribution shape and the variation amount of the energy of the pulsed light is simply referred to as “exposure unevenness”.

  FIG. 4 shows components obtained by removing definite unevenness from exposure unevenness. This is a non-uniform component caused only by the variation in energy of the pulsed light, and this is hereinafter referred to as “stochastic non-uniformity”.

  That is, the exposure unevenness does not coincide with the definite unevenness, and in the relationship between the exposure unevenness and the irradiation pulse, the offset component, the amplitude of the carrier component, and the like change according to the amount of variation in the energy of the pulsed light. Further, the variation in energy of the pulsed light also changes from moment to moment depending on the usage status of each optical member of the excimer laser and the exposure apparatus.

  As described above, in recent years, the number of pulsed light per unit period (annual) has increased with the improvement of the production capacity of the exposure apparatus, so the replacement cycle of the consumable module tends to be shortened. That is, the running cost tends to increase. In order to reduce the running cost, we want to save the number of pulsed lights to be irradiated without increasing exposure unevenness as much as possible.

  Based on the above discussion, in the present embodiment, the number of pulsed light necessary for the exposure unevenness to be within the allowable range is determined, and optimal exposure conditions (substrate scanning speed, pulsed light frequency, pulsed light are thus determined). A configuration for calculating at least one of the energy of light) is realized.

  FIG. 5 shows a schematic block diagram of an exposure apparatus in the present embodiment. The exposure apparatus according to this embodiment is a scanning exposure apparatus that transfers a pattern on a reticle onto a wafer by pulse illumination while scanning an original (reticle) and a substrate (wafer).

  The laser 1 includes a pulse discharge excitation gas laser such as an excimer laser and is a light source unit that supplies pulsed light. The light beam emitted from the laser 1 passes through the beam shaping unit 2, is shaped into a predetermined shape, and enters the light incident surface of the optical integrator 3. The optical integrator 3 is composed of a plurality of minute lenses, and a large number of secondary light sources are formed in the vicinity of the light exit surface.

  The diaphragm turret 4 limits the size of the surface of the secondary light source by a predetermined diaphragm. The aperture turret 4 is numbered (illumination mode number) such as an aperture stop having different circular aperture areas for setting a plurality of coherence factor σ values, a ring-shaped aperture for annular illumination, a quadrupole aperture, or the like. ) Multiple apertures are buried. Then, a diaphragm necessary for changing the shape of the incident light source of the illumination light is selected and inserted into the optical path. The first photoelectric conversion device 6 detects a part of the pulsed light reflected by the half mirror 5 as a light amount per pulse, and outputs an analog signal to the exposure amount calculation unit 21.

  The first condenser lens 7 Koehler-illuminates the blind 8 with a light beam from a secondary light source in the vicinity of the exit surface of the optical integrator 3. A slit 9 is provided in the vicinity of the blind 8, and the profile of the light illuminating the blind 8 is formed in a shape such as a rectangle or an arc. The slit light that has passed through the blind 8 and the slit 9 is a conjugate surface of the blind 8 via the second condenser lens 10 and the mirror 11, and the illuminance and the incident angle are uniformized on the reticle 13 on which the element pattern is formed. Imaging in the state. The opening area of the blind 8 is similar to the desired pattern exposure area of the reticle 13 in terms of the optical magnification ratio. During exposure, the blind 8 performs synchronous scanning with respect to the reticle stage 14 at an optical magnification ratio while shielding the outside of the exposure area of the reticle 13.

  The reticle 13 is held by a reticle stage 14. The slit light that has passed through the reticle 13 passes through the projection optical system 15 and is imaged again as slit light on the exposure field angle region on the pattern surface of the reticle 13 and the optical conjugate surface. The focus detection system 16 detects the height and inclination of the exposure surface on the wafer 18 held on the wafer stage 17. At the time of scanning exposure, the wafer stage 17 travels synchronously with the reticle stage 14 while being controlled so that the exposure surface of the wafer 18 coincides with the exposure field surface based on the information of the focus detection system 16. At the same time, the wafer 18 is exposed to slit light, and the pattern is transferred to the photoresist layer on the wafer 18. A second photoelectric conversion device 19 is installed on the wafer stage 17 and can measure the pulse light amount of slit light on the exposure field angle. The stage drive control unit 20 controls synchronous travel of the reticle stage 14 and the wafer stage 17 during scanning exposure including control of the exposure surface position.

  In the present embodiment, the control unit 30 includes a main control unit 22, an exposure amount calculation unit 21, a pulse energy variation measurement unit 27, an exposure error information holding unit 25, and a minimum irradiation pulse number calculation unit 26, which will be described below. . The exposure amount calculation unit 21 converts the electrical signal photoelectrically converted by the first photoelectric conversion device 6 and the second photoelectric conversion device 19 into a logical value and outputs the logical value to the main control unit 22. Note that the first photoelectric conversion device 6 is configured to allow measurement even during wafer exposure. The second photoelectric conversion device 19 detects the amount of slit light irradiated to the wafer 18 before the exposure process, and simultaneously obtains a correlation with the amount of light detected by the first photoelectric conversion device 6. Using this correlation, the main control unit 22 converts the output value of the first photoelectric conversion device 6 into a light amount on the wafer 18 and sets it as a light amount target value for exposure amount control.

  The laser control unit 23 outputs a trigger signal and an applied voltage signal according to the light amount target value, and controls the oscillation frequency and output energy of the laser 1. When the laser control unit 23 generates a trigger signal or an applied voltage signal, the light amount output value of the first photoelectric conversion device 6 acquired from the exposure amount calculation unit 21 or the exposure parameters ( Target integrated exposure amount, required integrated exposure amount accuracy, aperture shape, etc.) can be used. The exposure parameters are input and stored in the main controller 22 via the input device 24 as a man-machine interface or a media interface.

  The main control unit 22 calculates a parameter group necessary for exposure from data from the input device 24, parameters unique to the exposure device, and data measured by the first photoelectric conversion device 6 and the second photoelectric conversion device 19. Then, it is transmitted to the laser controller 23 and the stage drive controller 20. The pulse energy variation measuring unit 27 includes a measuring unit that measures the energy of the pulsed light acquired from the first photoelectric conversion device 6, and an evaluation value (for example, 30 pulses worth) of the energy variation amount for each pulse measured there. Standard deviation σ). This evaluation value can be updated in real time and stored in the memory within the pulse energy variation measuring unit 27. The measurement by the pulse energy variation measuring unit 27 may be performed during the exposure of the substrate, or may be performed during calibration between lots.

  Next, a method for calculating in advance the relationship between the number of irradiation pulses and exposure unevenness will be described. The light intensity distribution in the exposure area per pulse on the wafer 18 is measured by the second photoelectric conversion device 19 disposed on the wafer stage 17. The second photoelectric conversion device 19 is composed of a line sensor arranged in the scanning direction of the wafer 18 or a photo sensor capable of scanning in the scanning direction of the wafer 18, and its light receiving surface is an image plane of the projection optical system 15. It is arranged so that it almost matches.

  The main control unit 22 applies the number of irradiation pulses when the amount of energy variation of a certain pulsed light is added to the intensity distribution data of the exposure area per pulse obtained from the measurement result of the second photoelectric conversion device 19. Find the relationship with definite unevenness. FIG. 6 shows the relationship between the number of irradiation pulses and exposure unevenness when the energy variation (standard deviation σ value) is changed to 1%, 2%, and 3% for a specific intensity distribution. From the graph of FIG. 6, it can be seen that the offset component of exposure unevenness and the amplitude of the carrier component differ with respect to the number of irradiation pulses in accordance with the amount of energy variation. Next, for each energy variation amount, the number of pulse lights (minimum number of irradiation pulses) necessary for the exposure unevenness to be within an allowable range (for example, 0.6% or less) is obtained. Thereby, a correspondence relationship between the amount of energy variation and the minimum number of irradiation pulses is obtained. Here, by plotting the obtained minimum number of irradiation pulses on a graph in which the amount of energy variation is set on the horizontal axis and the minimum number of irradiation pulses is set on the vertical axis, the coefficient of the approximate curve of each plot (in the quadratic curve) When approximated, 0th order, 1st order, 2nd order coefficient) can be calculated. The calculated data of the coefficient of the approximate curve is stored in the exposure error information holding unit 25 which is a storage unit that can be configured by a memory or the like. Thus, according to this embodiment, the number of pulsed light can be determined based on the function showing the said correspondence.

  FIG. 7 shows an example of the structure of the coefficient table stored in the exposure error information holding unit 25. In the coefficient table, the coefficient of the approximate curve is described for each intensity distribution shape of the pulsed light that varies depending on the illumination mode. When the user registers a new illumination mode, the intensity distribution of the pulsed light also takes on a new shape. Therefore, a coefficient group of an approximate curve representing the relationship between the amount of energy variation and the minimum number of irradiation pulses is calculated again, and the coefficient table The coefficient information of the calculation result is added to.

  The minimum irradiation pulse number calculation unit 26 acquires the current measurement result of the energy variation from the pulse energy variation measurement unit 27. The minimum irradiation pulse number calculation unit 26 also acquires the intensity distribution shape of the pulsed light being used from the main control unit 22. The minimum irradiation pulse number calculation unit 26 further acquires an approximation coefficient corresponding to the intensity distribution shape of the pulsed light from the exposure error information holding unit 25. Then, the minimum irradiation pulse number calculation unit 26 calculates the currently optimal minimum irradiation pulse number from the acquired three pieces of information.

  The main control unit 22 acquires the currently optimal minimum irradiation pulse number calculated by the minimum irradiation pulse number calculation unit 26, and determines an exposure condition based on the minimum irradiation pulse number. The exposure conditions include at least one of reticle and wafer scanning speed, laser pulse oscillation frequency, and irradiation energy per pulse.

Second Embodiment
When calculating the exposure unevenness, a design value may be used as the intensity distribution to be used instead of the measurement result of the second photoelectric conversion device 19. When the design value is used, the intensity distribution shape of the pulsed light is uniquely determined by multiplying the “coherence factor σ value determined by the aperture turret 4” that can be set by the user and the “NA of the projection optical system”. Therefore, as shown in FIG. 8, a coefficient can be held for each “NA × σ”. When the coefficient table is held in the format shown in FIG. 8, for example, the coefficients are stored in advance at intervals of “NA × σ” value of 0.1. If “NA × σ” set by the user is between 0.1 intervals, a desired coefficient may be calculated by interpolating the stored coefficient values.

  Although the coefficient table in FIG. 8 corresponds only to the intensity distribution formed from the circular illumination shape, the coefficient table can be extended to a format as shown in FIG. In other words, by storing the coefficients when the horizontal axis is “NA × Outer σ” and the vertical axis is “NA × Inner σ” in a two-dimensional table, the coefficient when using any circular or annular illumination Can be expressed.

<Third Embodiment>
The third embodiment will be described with reference to FIG. This embodiment is different from the first and second embodiments described above in the manner of storing error information in the exposure error information holding unit 25 and the method of calculating the minimum irradiation pulse number in the minimum irradiation pulse number calculation unit 26.

  In the present embodiment, the minimum irradiation pulse number calculation unit 26 performs processes 1 to 6 shown in FIG. First, in process 1, deterministic unevenness (first exposure unevenness) in the intensity distribution of predetermined pulsed light is obtained and stored in the exposure error information holding unit 25. In the process 2, the exposure unevenness (second exposure unevenness) when the variation in unit energy (standard deviation σ = 1%) occurs in the intensity distribution of the pulsed light is obtained. In the process 3, the deterministic unevenness (first exposure unevenness) stored in the process 1 is subtracted from the second exposure unevenness obtained in the process 2 to thereby generate the stochastic unevenness (third exposure unevenness when the unit energy varies). ) And is stored in the exposure error information holding unit 25.

  Next, in process 4, the current energy variation measurement value is acquired from the pulse energy variation measurement unit 27, and the stochastic unevenness (first variation when the unit energy variation occurs in the intensity distribution of the desired pulsed light stored in process 3 (first step). 3 exposure unevenness) is acquired. Then, from these two pieces of information, the probabilistic unevenness (fourth exposure unevenness) caused by the variation in the energy of the current pulsed light is estimated. This stochastic unevenness is estimated by the following equation, for example.

En (p) = Eu (p) × (α × Sn / Su)
Here, En (p) represents the current stochastic unevenness (fourth exposure unevenness) at the number of irradiation pulses p. Eu (p) represents a stochastic non-uniformity (third exposure non-uniformity) at the time of occurrence of unit energy variation with the number of irradiation pulses p. α represents the effectiveness, Sn represents the current measured variation value of energy, and Su represents the variation amount of unit energy. The efficacy rate α may be handled as a fixed value that does not depend on the intensity distribution of the pulsed light. If the difference in the efficacy rate α that depends on the intensity distribution shape of the pulsed light cannot be allowed, the efficacy rate α is previously set for each intensity distribution. It may be calculated and stored in the exposure error information holding unit 25. In the process 5, the energy of the pulsed light is obtained by adding the deterministic unevenness (first exposure unevenness) acquired from the exposure error information holding unit 25 to the stochastic unevenness (fourth exposure unevenness) estimated as described above. The exposure unevenness (fifth exposure unevenness) that occurs due to the variation of the exposure is estimated. In process 6, the number of irradiation pulses (current minimum irradiation pulse number) necessary for the exposure unevenness (fifth exposure unevenness) estimated in process 5 to be within the allowable range is obtained. As described above, the fluctuation amount corresponding to the variation amount obtained by the measurement unit is estimated based on the variation amount per unit amount of the variation amount of the energy of the pulsed light.

  The main control unit 22 obtains the currently optimal minimum irradiation pulse number from the minimum irradiation pulse number calculation unit 26, and similarly to the first and second embodiments, the wafer exposure conditions (reticle and wafer scanning speed, laser pulse oscillation frequency). (Irradiation energy per pulse) is determined.

  The operation of the embodiment has been described above. If the exposure condition determination method according to the above embodiment is used, substrate exposure can be performed with the minimum number of irradiation pulses that allow exposure unevenness in accordance with the amount of energy variation of the current pulsed light. This makes it possible to reduce running costs while maintaining the device performance.

  Further, as shown in the left diagram of FIG. 11, since the intensity distribution shape of the pulsed light differs depending on the position in the X direction in the shot exposure region, the exposure unevenness at each X position also differs. Therefore, in order to fall below the exposure unevenness tolerance in the entire area within the shot, the minimum number of irradiation pulses may be calculated based on the maximum value of the exposure unevenness calculated at each X position.

  Further, as shown in the left diagram of FIG. 12, even if the variation amount of the same energy (the standard deviation σ value is the same), the carrier amplitude of the exposure unevenness varies depending on the variation state. Therefore, in order to eliminate the influence due to the difference in the variation state, the minimum number of irradiation pulses may be calculated based on the maximum value of the exposure unevenness calculated in the pulse train of the plurality of variation states.

  According to the embodiment described above, the minimum number of irradiation pulses can be calculated accurately, and the number of pulses used during substrate exposure can be saved. That is, it is not necessary to use an excessive number of pulses for an allowable exposure unevenness amount. Thereby, the lifetime of the internal module of a light source part can be anticipated.

<Embodiment of Method for Manufacturing Article>
The method for manufacturing an article according to an embodiment of the present invention is suitable for manufacturing an article such as a microdevice such as a semiconductor device or an element having a fine structure. In the method for manufacturing an article according to the present embodiment, a latent image pattern is formed on the photosensitive agent applied to the substrate using the above-described exposure apparatus (a step of exposing the substrate), and the latent image pattern is formed in this step. Developing the substrate. Further, the manufacturing method includes other well-known steps (oxidation, film formation, vapor deposition, doping, planarization, etching, resist stripping, dicing, bonding, packaging, and the like). The method for manufacturing an article according to the present embodiment is advantageous in at least one of the performance, quality, productivity, and production cost of the article as compared with the conventional method.

20: Stage drive control unit, 21: Exposure amount calculation unit, 22: Main control unit, 23: Laser control unit, 25: Exposure error information holding unit, 26: Minimum irradiation pulse number calculation unit, 27: Pulse energy variation measurement unit

Claims (10)

An exposure apparatus that scans and exposes a substrate using pulsed light supplied from a light source unit,
A measurement unit for measuring the energy of the pulsed light;
A control unit for determining the number of the pulsed light irradiated on the substrate while the substrate moves a unit length in the scanning direction,
The said control part determines the said number based on the variation amount of the said energy. The exposure apparatus characterized by the above-mentioned.   The exposure apparatus according to claim 1, wherein the controller determines the number based on a correspondence relationship obtained in advance between the variation amount and the number.   The exposure apparatus according to claim 2, wherein the number in the correspondence relationship is the number of the pulsed light necessary to keep the variation amount of the exposure amount within an allowable range.   The exposure apparatus according to claim 2, wherein the control unit determines the number based on a function representing the correspondence relationship.   5. The control unit according to claim 1, wherein the control unit determines at least one of a scanning speed of the substrate, a frequency of the pulsed light, and an energy of the pulsed light based on the number. 2. The exposure apparatus according to item 1.   The exposure apparatus according to claim 2, further comprising a storage unit that stores information regarding the correspondence relationship.   The exposure apparatus according to claim 6, wherein the storage unit stores the information for each intensity distribution of the pulsed light.   The said control part performs the estimation of the said variation | change_quantity corresponding to the variation | change_quantity obtained by the said measurement part based on the said variation | change_quantity per unit amount of the said variation | change_quantity. Exposure device.   The exposure apparatus according to claim 8, wherein the estimation is performed based on an intensity distribution of the pulsed light. A step of exposing the substrate using the exposure apparatus according to any one of claims 1 to 9,
Developing the substrate exposed in the step;
A method for producing an article comprising:

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