JP2011129653A - Measurement method and exposure apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately measure imaging characteristics in a projection optical system, in particular, angle characteristics of exposure light. <P>SOLUTION: An angular distribution of exposure light exposing a substrate is measured using an exposure apparatus having an illumination optical system that illuminates a mask using light from a light source and a projection optical system that projects a mask pattern on the substrate. A specific pattern having a line width of λ×10/(NA×β) or more, wherein λ represents a wavelength of the light source, NA represents an injection side numerical aperture on an emission side in the projection optical system, and β represents a projection magnification ratio of the projection optical system, is arranged on an object surface of the projection optical system, the specific pattern is illuminated, images of the specific pattern at a plurality of positions in the optical axis direction of the projection optical system are measured using a sensor, and angle characteristics of the exposure light are calculated using the measured result. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a measurement method and an exposure apparatus.

  2. Description of the Related Art When a semiconductor element is manufactured using a photolithography technique, a projection exposure apparatus that projects a circuit pattern drawn on a mask (reticle) onto a wafer or the like by a projection optical system and transfers the circuit pattern is used.

  In the lithography process, when a circuit pattern is superimposed on a wafer, the overlay accuracy between the pattern already formed on the wafer and the pattern drawn thereon is important. A technique for adjusting the effective light source distribution has attracted attention as one of the measures for improving the overlay accuracy (see Patent Documents 1 and 2). The effective light source distribution means the angular distribution of the exposure light beam incident on the wafer surface, and is also the light intensity distribution on the pupil plane of the projection optical system.

  Conventionally, while controlling the effective light source distribution adjusting means, the wafer is exposed and developed using a measurement mask on which predetermined measurement marks are formed, and the shape (position and size) of the resist image formed on the wafer is measured. Etc.). A method of calculating imaging characteristics such as angle characteristics that affect the overlay accuracy using the measurement result has been used. For this reason, it takes a lot of time for exposure, development and measurement. As an alternative, there is a method of measuring imaging characteristics that affect the overlay accuracy by observing the light intensity distribution (aerial image) on the image plane of the projection optical system (see Patent Document 3).

Japanese Patent Laid-Open No. 05-217853 JP 2007-36016 A Japanese Patent Laid-Open No. 2003-218024

  However, in the method described in Patent Document 3, there is no description of the relationship between the NA of the projection optical system and the line width of the pattern of the measurement mask, and highly accurate measurement is performed, for example, when the NA of the projection optical system is large. I can't.

  Accordingly, an object of the present invention is to measure with high accuracy the imaging characteristics of a projection optical system, particularly the angular characteristics of exposure light.

  According to another aspect of the present invention, there is provided a measurement method using an exposure apparatus having an illumination optical system that illuminates a mask using light from a light source and a projection optical system that projects a pattern of the mask onto the substrate. Is a measurement method for measuring the angular distribution of exposure light for exposing the projection optical system, wherein the wavelength of the light source is λ, the exit numerical aperture of the projection optical system is NA, and the projection magnification of the projection optical system is β. Arranging a specific pattern having a line width of λ × 10 / (NA × β) or more on the object plane of the system, illuminating the specific pattern, and the specific pattern at a plurality of positions in the optical axis direction of the projection optical system A step of measuring the image using a sensor, and a step of calculating an angle characteristic of the exposure light using the measurement result.

  An exposure apparatus according to one aspect of the present invention measures an illumination optical system that illuminates a mask using light from a light source, a projection optical system that projects the mask pattern onto a substrate, and an image of the mask pattern. In an exposure apparatus having a sensor and a control unit that calculates angle characteristics of exposure light using measurement data from the sensor, the mask or a mask stage that holds the mask has a plurality of measurement widths different from each other. A pattern is formed, where the wavelength of the light source is λ, the exit numerical aperture of the projection optical system is NA, and the projection magnification of the projection optical system is β, the control unit is λ × 10 / of the measurement pattern. The driving of the mask stage is controlled so that a specific pattern having a line width of (NA × β) or more is illuminated, and the specific pattern at a plurality of positions in the optical axis direction of the projection optical system is controlled. The using the measurement result obtained by the sensor is measured, and calculates the angular characteristics of the exposure light for exposing the substrate.

  According to the present invention, it is possible to measure the imaging characteristics of the projection optical system, particularly the angular characteristics of exposure light, with high accuracy.

It is the schematic of the exposure apparatus in 1st Example of this invention. It is a figure showing the pattern for a measurement. It is a figure showing the pattern for a measurement. It is a figure of the light intensity distribution which changes with defocus distance. It is a figure of the light intensity distribution for demonstrating calculation of the amount of position shifts. It is a figure explaining light intensity distribution when NA changes. It is a figure explaining the relationship between the line width of a pattern, and an angle characteristic. It is a measurement flowchart of an angle characteristic.

Example 1
A first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic view of an exposure apparatus in this embodiment.

  The light source 1 is, for example, an ArF excimer laser having a wavelength of about 193 nm or a KrF excimer laser having a wavelength of about 248 nm. The routing optical system 2 guides the light beam from the light source 1 to the diffractive optical element 3.

  The diffractive optical element 3 is mounted on a turret having a plurality of slots, and an arbitrary diffractive optical element can be moved on the optical axis by an actuator 4. The light emitted from the diffractive optical element 3 is collected by the condenser lens 5 to form a diffraction pattern on the diffraction pattern surface 6. The diffraction pattern can be changed by exchanging the diffractive optical element located on the optical axis by the actuator 4. The diffraction pattern formed on the diffraction pattern surface 6 is incident on the mirror 9 after the light beam cross-sectional shape (ring zone ratio, outer diameter, etc.) is adjusted by the prism 7 and the zoom lens 8.

  The light beam reflected by the mirror 9 enters the light intensity distribution forming means 10. In this embodiment, the light intensity distribution forming means 10 is a lens array. The prism 7 can be zoomed. When the distance between the prisms 7a and 7b is sufficiently small, the prisms 7a and 7b can be regarded as a single piece of parallel flat glass. At this time, the diffraction pattern formed on the diffraction pattern surface 6 is adjusted in the light beam diameter (σ value) by the enlargement / reduction of the zoom lens 8 while maintaining a substantially similar shape, and forms an image on the incident surface of the light intensity distribution forming means 10. Is done. Further, the diffraction pattern formed on the diffraction pattern surface 6 is adjusted by separating the positions of the prisms 7a and 7b.

  The emitted light beam of the light intensity distribution forming means 10 is condensed by the condenser lens 11 and illuminates the surface on which the light shielding member 13 is arranged (surface conjugate with the irradiated surface) with a desired light intensity distribution. The light shielding member 13 defines the illumination range of the mask 17 arranged on the irradiated surface, and the operation is controlled in synchronization with the scanning of the mask stage 21 holding the mask 17 and the wafer stage 19 holding the wafer.

  The light shielding member 12 is disposed at a position defocused from the surface on which the light shielding member 13 is disposed, and has a trapezoidal light intensity distribution (vertical axis: light intensity, horizontal axis: luminous flux) on the surface where the light shielding member 13 is disposed. Position in the cross section). By making the light intensity distribution trapezoidal, it is possible to avoid unevenness in the accumulated exposure amount in the scanning direction due to pulse discontinuity when the wafer is exposed. Further, by changing the opening width of the light shielding member 12 in the direction corresponding to the scanning direction of the stage, the unevenness of the integrated exposure amount accumulated in the scanning direction for each image height in the X direction (direction perpendicular to the scanning direction). Can be avoided.

  The light that has passed through the light shielding member 13 illuminates the mask 17 through the lens 14, the mirror 15, and the lens 16. The pattern image of the mask 17 is exposed to the wafer held on the wafer stage 19 by the projection optical system 18.

  The sensor 20 is a CCD sensor or a photodiode sensor that can detect the amount of light. The sensor 20 is disposed on the wafer stage 19 and is positioned at the image plane of the projection optical system 18 or a position defocused from the image plane, receives light from the projection optical system, and receives the light intensity of exposure light ( Illuminance) can be measured.

  Next, a measurement pattern for measuring the angle characteristic of exposure light will be described. The measurement pattern is formed on a measurement mask or mask stage 21.

  FIG. 2 shows an example of a measurement pattern formed on the measurement mask. In FIG. 2, black represents a light shielding portion and white represents a light transmission portion (opening portion). However, the reverse is also possible. The pattern shown in FIG. 2A is a pattern for measuring the angular distribution characteristics in the X direction (direction perpendicular to the scanning direction) of the irradiation light that irradiates the wafer, and a plurality of light transmission portions each having a different line width. including. Note that the term “measurement pattern” is not limited to a plurality of light transmission parts, and is used to mean only one light transmission part.

  In this embodiment, as will be described later, a light transmissive portion (pattern) having a line width of λ × 10 / (NA × β) or more is selected from a plurality of light transmissive portions and illuminated. It is assumed that the wavelength of the light source 1 is λ, the exit numerical aperture of the projection optical system 18 is NA, and the projection magnification of the projection optical system 18 is β. Therefore, when the NA of the projection optical system 18 is changed, the selected pattern is changed according to the NA of the projection optical system 18.

  The pattern shown in FIG. 2B is a pattern for measuring the angular distribution characteristics in the Y direction (scanning direction) of the irradiation light that irradiates the wafer, and a plurality of light transmission parts (openings) each having a different line width. Have Similar to the measurement pattern shown in FIG. 2, a light transmission portion having a line width of λ × 10 / (NA × β) or more is selected according to the NA of the projection optical system.

  FIG. 3A shows another example of the measurement pattern. The pattern shown in FIG. 3A is a pattern for measuring the angular distribution characteristics in the X direction (direction perpendicular to the scanning direction) of the irradiation light that irradiates the wafer. The pattern shown in FIG. 3A includes a plurality of groups having different line widths for each group, with a plurality of light transmission portions (openings) having the same line width as one group (pattern). Also in this case, a pattern having a line width of λ × 10 / (NA × β) or more is selected according to the NA of the projection optical system.

  If the measurement pattern shown in FIG. 3A is used instead of the pattern shown in FIG. 2, the total light amount detected by the sensor is improved, and the influence of noise can be reduced. Moreover, the influence of the line width error due to the manufacture of the light transmission part can also be reduced.

  The light transmission part of the measurement pattern is not limited to the rectangle shown in FIGS. 2 and 3A, but may be a square. In the case of a square, the angular distribution characteristic in the X direction and the angular distribution characteristic in the Y direction can be acquired with only a square pattern formed on one mask (mask stage).

  The size of the space arranged on the mask (interval between the light transmitting portions) must be such that aerial images corresponding to the light transmitting portions do not overlap each other, and at least represents (NA / β × measurement position). Defocus distance from the image plane). The defocus distance represents a distance from the image plane in the optical axis direction of the projection optical system.

  When measuring the angular characteristics of the exposure light, the illumination optical systems 2 to 16 use the light from the light source 1 by placing a measurement pattern on the irradiated surface (the object surface of the projection optical system 18). Illuminate the pattern. An image of the measurement pattern is projected onto the image plane by the projection optical system 18, and a light intensity distribution (aerial image) is formed on the image plane. At this time, the aerial image is measured using the sensor 20 at a plurality of positions in the image plane or in the vicinity of the image plane (a plurality of positions in the optical axis direction of the projection optical system 18). Then, the angle characteristic of the exposure light is calculated using the measurement result.

  When the sensor 20 is a CCD sensor, the measurement accuracy can be improved by emitting the pulsed light from the laser light source a plurality of times and calculating the average value of the plurality of light intensity distributions. When the sensor 20 is a photodiode, a waveform can be acquired by placing a slit on the image plane and scanning. However, since an error is added to the measurement value due to stage vibration or stage operation error during scanning, it is desirable to use a value obtained by averaging the measurement results obtained by scanning a plurality of times.

  FIG. 3B shows an example of slits arranged on the image plane when the measurement pattern shown in FIG. 3A is used and a photodiode is used as the sensor 20. In the member shown in FIG. 3B, slits (white portions) are formed corresponding to the positions of the measurement pattern shown in FIG. The smaller the slit width, the better the aerial image can be measured. However, if the slit width is too small, the amount of light incident on the photodiode becomes small, and therefore an error due to sensor noise is received.

  An example of the light intensity distribution acquired by the sensor 20 is shown in FIG. The light intensity distribution varies depending on the line width of the measurement pattern, the angular distribution of the exposure light, and the measurement position (defocus distance) of the sensor 20. FIG. 4 shows the change in the light intensity distribution when only the defocus distance is changed. At the best focus position, the curve is steep at a position of 5 μm on the XY plane, but the curve becomes gentler as the defocus distance increases.

  Further, when the angular distribution of the exposure light changes, the position in the XY plane of the entire light intensity distribution shifts (shifts) at the defocus position. Therefore, the angular distribution of the exposure light can be calculated using the positional deviation amount and the defocus distance.

  FIG. 5 shows the light intensity distribution measured at a certain defocus distance. First, a specified range that represents the characteristics of the light intensity distribution and can reduce the influence of sensor noise (for example, a range surrounded by a thick square frame in FIG. 5), the light intensity is equal to or higher than the first specified value, and the second specified value. The barycentric position of the light intensity distribution is obtained within the range below the value. The position of the center of gravity is defined as a positional deviation amount in the XY plane. Next, the defocus distance is changed, the light intensity distribution is similarly measured, and the center of gravity position is obtained. Then, the angle characteristic T is calculated by dividing the difference in the amount of displacement by the difference in the defocus distance. Expressed by the equation, T = (position shift amount 1−position shift amount 2) / (defocus distance 1−defocus distance 2). Note that the positional deviation amount is not limited to the position of the center of gravity, and other indices can be used.

  Here, as the measurement error of the positional deviation amount, stage vibration, sensor measurement error, vibration of other devices, and the like are conceivable. In order to reduce the measurement error of the positional deviation amount, it is necessary to increase the sensor defocus distance. To that end, a line width measurement pattern that can measure the aerial image at the position where the sensor is defocused is required. is necessary.

  Also, in the case of a line width of λ × 10 / (NA × β) or less, the defocus distance used for the measurement is small, and the amount of positional deviation of the image due to the influence of the aberration of the projection optical system is large. I can't measure.

  Furthermore, the larger the NA of the projection optical system, the larger the change in the shape of the aerial image with respect to the defocus distance, so it is better to use a measurement pattern with a larger line width.

  FIG. 6 shows the NA of the projection optical system (NA of the irradiation light of the wafer) and the shape change of the aerial image. FIG. 6A shows an image when a light transmitting portion (opening) having a line width of 10 μm formed on the mask 17 is illuminated under the conditions of λ = 193 nm, NA = 0.3, and a defocus distance of 0 to 7 μm. It is a signal waveform detected by the surface sensor 20. FIG. 6B shows a signal waveform when the conditions other than NA are the same as those shown in FIG. 6A and NA is 0.85. FIG. 6 shows that the larger the NA, the greater the change in waveform with respect to the change in defocus distance.

  FIG. 7 is a graph showing the relationship between the line width of the light transmitting portion and the calculated T. In the measurement for obtaining the data shown in FIG. 7, the value of the angle characteristic T is set with nonuniformity in the irradiation angle distribution of the illumination optical device, and the line width (μm) of the light transmission part is changed. The measurement conditions are λ = 193 nm, NA = 0.93, and β = 1/4.

  FIG. 7 shows that the angle characteristic T increases as the line width decreases and deviates from the true value. The absolute value of T when the line width is 2 μm is about ¼ of the absolute value of T when the line width is λ × 10 / (NA × β) = 8.3 μm. When the line width is λ × 10 / (NA × β) or less, measurement errors such as stage vibrations, sensor measurement errors, and apparatus vibrations are easily received, thereby increasing T measurement errors.

  Therefore, by using a light transmission portion having a line width of λ × 10 / (NA × β) or more, the defocus distance can be increased, and the angle characteristic can be measured with high accuracy.

  Therefore, in this embodiment, a light transmission portion having a line width of λ × 10 / (NA × β) or more from a plurality of light transmission portions (patterns) formed on a mask or a mask stage as a measurement pattern. Select (Pattern) and illuminate.

  A method for measuring the angle characteristic of exposure light using the above-described measurement pattern will be described with reference to the measurement flowchart of FIG. First, the control unit 22 acquires data on the wavelength of the light source, the NA of the projection optical system, and the magnification (S101). Then, the control unit 22 selects a pattern having a line width of λ × 10 / (NA × β) or more from the measurement patterns, and the selected pattern (specific pattern) enters the illumination area. The drive (actuator) of the mask stage 21 is controlled. Further, the control unit 22 controls the driving of the wafer stage 19 to place the sensor 20 in the exposure area (S102). Then, a pattern having a line width of λ × 10 / (NA × β) or more is illuminated (S103), and the aerial image projected by the projection optical system 18 is measured by the sensor 20 at a certain defocus distance. Next, the same measurement is performed by changing the defocus distance. That is, the aerial image is measured at a plurality of positions (defocus distances) (S104). Measurement data and defocus distance data obtained by the sensor 20 are output to the control unit 22. The arithmetic processing unit of the control unit 22 calculates the positional deviation amount of the light intensity distribution using the measurement data, and further calculates the angle characteristic T from the above formula using the defocus distance data (S105).

  In addition, the measurement result of the angle characteristic of exposure light can be used for adjustment of an exposure apparatus. For example, based on the measurement result of the angle characteristic, the position and angle of at least one of the angle illumination optical system and the projection optical system may be adjusted using the desired angle characteristic as a target value. In addition, the exposure apparatus (illumination optical system, projection optical system, etc.) is set in a plurality of different states, the angular characteristics of the irradiated light are measured, and the exposure apparatus is adjusted to a state where the value of the angular characteristics is smaller. As a method of adjustment, the method described in Patent Document 1 or 2 can also be used.

  As described above, according to the present embodiment, the angular characteristics of the exposure light can be measured with high accuracy.

(Example 2)
Next, a method for manufacturing a device (semiconductor IC element, liquid crystal display element, etc.) using the above-described exposure apparatus will be described.

  First, the angular distribution of exposure light is measured using the exposure apparatus described above. Then, the angular distribution of the exposure light is adjusted by controlling each optical system of the exposure apparatus using the measurement result. Then, using the adjusted exposure apparatus, the above-described exposure apparatus is used to expose a substrate (wafer, glass substrate, etc.) coated with a photosensitive agent, and the substrate (photosensitive agent) is developed. A device is manufactured through a process and other known processes. Other known processes include etching, resist stripping, dicing, bonding, packaging, and the like. According to this device manufacturing method, it is possible to manufacture a higher quality device than before.

17 Mask 18 Projection Optical System 19 Wafer Stage 20 Sensor 21 Mask Stage 22 Control Unit

Claims (6)

An angular distribution of exposure light that exposes the substrate is measured using an exposure apparatus that includes an illumination optical system that illuminates the mask using light from a light source and a projection optical system that projects the pattern of the mask onto the substrate. A measuring method,
A line width of λ × 10 / (NA × β) or more on the object plane of the projection optical system, where λ is the wavelength of the light source, NA is the exit numerical aperture of the projection optical system, and β is the magnification of the projection optical system. Placing a specific pattern of
Illuminating the specific pattern using the illumination optical system, and measuring images of the specific pattern at a plurality of positions in the optical axis direction of the projection optical system using a sensor;
And a step of calculating an angle characteristic of the exposure light using the measurement result.   A method for adjusting an illumination optical system, wherein the illumination optical system is set in a plurality of different states, the measurement method according to claim 1 is performed, and the illumination optical system is adjusted using the measurement result. .   A method for adjusting a projection optical system, wherein the projection optical system is set in a plurality of different states, the measurement method according to claim 1 is performed, and the projection optical system is adjusted using the measurement result. . In an exposure apparatus having an illumination optical system that illuminates a mask using light from a light source, a projection optical system that projects a pattern of the mask onto a substrate, and a sensor that receives light from the projection optical system,
A plurality of measurement patterns having different line widths are formed on the mask stage or measurement mask holding the mask,
The exposure apparatus includes:
Specifying a line width of λ × 10 / (NA × β) or more in the measurement pattern, where λ is the wavelength of the light source, NA is the exit numerical aperture of the projection optical system, and β is the magnification of the projection optical system The angle of the exposure light that exposes the substrate using the measurement results obtained by the sensor measuring the images of the specific pattern at a plurality of positions in the optical axis direction of the projection optical system with the pattern illuminated. An exposure apparatus having a control unit for calculating characteristics.   The exposure apparatus according to claim 1, wherein at least one of the illumination optical system and the projection optical system is adjusted using the calculated angular characteristic. Exposing the substrate using the exposure apparatus according to claim 5;
And developing the exposed substrate. A device manufacturing method comprising:

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