JP2008066565A - Exposure method and exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently prevent variations generating in a pattern dimension after processing even when a spectrum width such as a half-width or the like varies in laser beams illuminating on a photomask formed with a mask pattern, and to enhance a product yield and a throughput. <P>SOLUTION: A photoresist film PR on which a mask pattern image is projected is developed, whereby shape information of a resist pattern formed on a wafer W is obtained. When an exposure is carried out, a polarizing state of the laser beams illuminating on a photomask PM is adjusted based on the shape information of the obtained resist pattern so that a shape of the resist pattern is formed corresponding to a design pattern. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exposure method and an exposure apparatus, and more particularly, to illuminate a photomask on which a mask pattern is formed and to expose a mask pattern image generated by the illumination onto a photoresist film formed on a wafer. About.

  In manufacturing a semiconductor device, a fine pattern is processed using a lithography technique.

  Here, for example, after a photoresist film made of a photosensitive material is formed on the surface to be patterned, a photomask having a mask pattern formed on the design pattern is illuminated, and a mask pattern image generated by the illumination is illuminated. The photoresist film formed on the wafer is exposed and transferred. Thereafter, the photoresist film to which the mask pattern image has been transferred is developed to form a resist pattern on the surface of the wafer. Then, patterning is performed by performing an etching process using the resist pattern as a mask.

  In the lithography technique, it is required to finely process a pattern with higher resolution in order to meet the demand for higher integration of devices and higher operation speed. This resolution R is expressed by the following formula (1) by the wavelength λ of the light irradiated from the light source to the photomask and the numerical aperture NA of the projection lens that projects the mask pattern image of the photomask onto the resist film. Thus, it is determined by the Rayleigh equation. Here, k is a constant and is determined according to the process.

[Equation 1]
R = k · λ / NA (1)

  As shown in this equation (1), the resolution R increases as the wavelength λ of the light from the laser light source becomes shorter and the numerical aperture NA of the projection lens increases. Therefore, the resolution is improved by reducing the wavelength λ of the light from the light source and increasing the numerical aperture NA of the projection lens.

  For example, with regard to the light source, the KrF excimer laser having a wavelength of 248 nm is shifted to an ArF excimer laser having a wavelength of 193 nm, thereby improving the resolution.

  On the other hand, the numerical aperture NA of the projection lens is approaching 1 which is the theoretical limit. For this reason, an immersion exposure method has been proposed in which the space between the projection lens and the photoresist film is filled with a liquid such as pure water to increase the effective numerical aperture NA (see, for example, Patent Document 1).

  That is, the numerical aperture NA is expressed by the following formula (2) by the refractive index n of the medium through which the light passes and the angle θ formed by the light. 1. The medium in the space between the projection lens through which the lens passes and the resist film is replaced with air having a refractive index n of 1, for example, by pure water having a refractive index n of 1.44, thereby increasing 1.44 times. The numerical aperture NA can be realized and the resolution R can be improved.

[Equation 2]
NA = n × sin θ (2)

  Also, a method for adjusting the polarization state of the laser light that illuminates the photomask has been proposed in order to cope with an increase in the degree of contrast degradation due to the polarization state as the numerical aperture NA increases ( For example, see Patent Document 2).

  In addition, since it may be difficult to process a pattern corresponding to a design pattern by OPE (Optical Proximity Effect), OPC (Optical Proximity Correction) is applied to the mask pattern.

JP 2005-57278 A Japanese Patent Laid-Open No. 2005-5521

  However, in the lithography process, there may be a variation in dimensions in the processed pattern. For example, a CD (Critical Dimension) difference increases between a rough (Isolated) pattern and a dense (Dense) pattern, and so-called “Iso Sense Bias (IDS)” may occur.

  This is because, in the laser light emitted from the laser light source, the spectral width such as the half-value width fluctuates and the chromatic aberration changes, resulting in variations in the image formation position of the transferred mask pattern image. In other words, even when exposure is performed using a photomask on which a mask pattern subjected to OPC is formed, such a problem may occur because the OPE fluctuates. For this reason, the product yield may decrease and it may be difficult to improve the throughput.

  Therefore, it has been difficult to efficiently prevent variations in pattern dimensions after processing and to improve product yield and throughput.

  Accordingly, it is an object of the present invention to provide an exposure method and an exposure apparatus that can prevent variations in pattern dimensions after processing, improve product yield, and improve throughput.

  In order to solve the above problems, an exposure method of the present invention irradiates a photomask on which a mask pattern is formed with a laser beam, and forms a mask pattern image generated on the wafer by the photomask illuminated with the laser beam. An exposure method for performing exposure by projecting onto a formed photoresist film, wherein the photoresist film on which the mask pattern image is projected is developed to obtain shape information of a resist pattern formed on the wafer A resist pattern shape information acquisition step, and when performing the exposure, the resist pattern shape acquired in the resist pattern shape information acquisition step so that the shape of the resist pattern is formed corresponding to the design pattern Based on the information, the polarization state of the laser light that illuminates the photomask is changed.

  In order to solve the above-described problems, an exposure apparatus of the present invention is generated by an illumination optical system that illuminates laser light onto a photomask on which a mask pattern is formed, and the photomask that is illuminated with laser light by the illumination optical system. A projection optical system that projects a mask pattern image onto a photoresist film formed on a wafer, and the photoresist film on which the mask pattern image is projected by the projection optical system is developed to form the wafer on the wafer. An exposure apparatus having a resist pattern shape information acquisition unit that acquires shape information of a resist pattern, wherein the illumination optical system includes a polarization state adjustment unit that changes a polarization state of the laser light, and the polarization state adjustment unit The resist pattern is formed so that the shape of the resist pattern corresponds to the design pattern. Based on the resist pattern shape information obtained by chromatography emissions shape information acquiring unit, changes the polarization state of the laser light.

  According to the present invention, it is possible to provide an exposure method and an exposure apparatus that prevent variations in pattern dimensions after processing, improve product yield, and improve throughput.

  Embodiments according to the present invention will be described.

  FIG. 1 is a block diagram showing an exposure apparatus 1 in Embodiment 1 according to the present invention.

  As shown in FIG. 1, the exposure apparatus 1 of the present embodiment includes a photomask support unit 11, a wafer support unit 21, a laser light source 31, an illumination optical system 40, a projection optical system 51, and a polarization monitor unit 61. And a control unit 71 and a resist pattern shape information acquisition unit 81. Each part will be described sequentially.

  As shown in FIG. 1, the photomask support 11 includes a stage and supports a photomask PM on which a mask pattern is formed. The photomask support unit 11 fixes the photomask PM transported from the outside of the apparatus by a mask transport system (not shown), for example, by vacuum suction. The photomask support 11 is provided with a reflecting mirror (not shown), and its position and inclination are detected by a laser interferometer (not shown) installed so as to correspond to the reflecting mirror. The photomask support unit 11 includes a drive motor (not shown), and the x direction along the surface of the photomask PM that supports the photomask PM, and the y direction orthogonal to the x direction on the surface of the photomask PM. Then, it is moved by a drive motor in each of the z direction perpendicular to the surface of the photomask PM. Then, the photomask PM is rotated by a drive motor, and the inclination of the surface of the photomask PM is adjusted. Here, the controller 71 controls the drive motor based on the position and inclination of the photomask support 11 detected by the laser interferometer, and the position and inclination of the photomask support 11 are adjusted.

  As shown in FIG. 1, the wafer support unit 21 includes a stage and supports the wafer W on which the photoresist film PR is formed on the stage. Specifically, the wafer support portion 21 is coated with a photoresist solution by a resist coating apparatus (not shown), and pre-baked by a heat treatment apparatus (not shown) to form a photoresist film PR. The wafer W is transferred from the outside by a wafer transfer system (not shown). Then, the wafer W on which the photoresist film PR is formed is fixed, for example, by vacuum suction. Further, the wafer support unit 21 is provided with a reflecting mirror (not shown), and its position and inclination are detected by a laser interferometer (not shown) installed so as to correspond to the reflecting mirror. The wafer support unit 21 includes a drive motor (not shown), the x direction along the surface of the wafer W that is supported, the y direction perpendicular to the x direction on the surface of the wafer W, and the wafer. It is moved by the drive motor in the respective directions of the z direction perpendicular to the surface of W. The surface of the wafer W is adjusted by rotating the wafer W in the rotational directions of the respective axes in the x, y, and z directions by the drive motor. Here, the controller 71 controls the drive motor based on the position and tilt of the wafer support 21 detected by the laser interferometer, and the position and tilt of the wafer support 21 are adjusted.

As shown in FIG. 1, the laser light source 31 emits laser light. The laser light source 31 includes, for example, an ArF excimer laser light source, and emits laser light having a wavelength of 193 nm to the illumination optical system 40. Here, laser light that is substantially linearly polarized light and is narrowed so that the half-value width is 1 pm or less is emitted. In addition, the laser light source 31 may be configured by a light source such as a KrF laser or an F ₂ laser.

  As shown in FIG. 1, the illumination optical system 40 includes a relay optical system 141, a polarization state adjusting unit 142, a beam shape shaping unit 143, an optical integrator 144, a beam splitter 145, a condenser lens 146, an aperture stop. 147, an imaging lens 148, and a mirror 149. In the illumination optical system 40, each unit includes a drive system, and the drive system drives each unit based on a command from the control unit 71, and the laser light emitted from the laser light source 31 is supplied to the photomask support unit 11. Illuminate the photomask PM supported by.

  Specifically, in the illumination optical system 40, the relay optical system 141 relays the laser light emitted from the laser light source 31 to the polarization state adjusting unit 142.

  Then, the polarization state adjustment unit 142 adjusts the polarization state of the laser light and emits it to the beam shaping unit 143. Here, as shown in FIG. 1, the polarization state adjusting unit 142 includes a quarter-wave plate 142a and a half-wave plate 142b. Each of the quarter wavelength plate 142a and the half wavelength plate 142b is arranged so as to be rotated around the optical axis of the incident laser light. The polarization state is adjusted by rotationally driving the four-wave plate 142a and the half-wave plate 142b. That is, the ellipticity of the laser beam is adjusted by rotating the quarter wavelength plate 142a, and the main axis azimuth angle of the laser beam is adjusted by rotating the half wavelength plate 142b. Although details will be described later, in the present embodiment, the polarization state adjustment unit 142 performs the previous exposure so that the shape of the resist pattern is formed corresponding to the design pattern when performing the exposure. Based on the resist pattern shape information acquired later by the resist pattern shape information acquiring unit 81, the polarization state of the laser light is adjusted.

  The laser beam emitted by the polarization state adjusting unit 142 is shaped by the beam shaping unit 143 and emitted to the optical integrator 144.

  Then, the optical integrator 144 converts this laser light. Here, the optical integrator 144 includes a fly array lens, and the fly array lens converts the incident laser light into a secondary light source and emits it to the beam splitter 145.

  Then, the beam splitter 145 divides the laser light into a condenser lens 146 side and a polarization monitor unit 61 side. Here, the beam splitter 145 is configured as a half mirror, transmits the laser light emitted from the laser light source 31, emits the laser light to the condenser lens 146 side, and emits the laser light emitted from the laser light source 31. The light is reflected and emitted to the polarization monitor unit 61 side.

  The laser light emitted from the beam splitter 145 is condensed by the condenser lens 146 and emitted to the aperture stop 147.

  The laser beam is shaped by the aperture stop 147 partially blocking the light, and emitted to the imaging lens 148.

  Then, the imaging lens 148 forms an image of the laser light on the photomask PM supported by the photomask support 11 via the mirror 149.

  As shown in FIG. 1, the projection optical system 51 includes a projection lens group 52 and an aperture stop 53, and a mask pattern image generated by the photomask PM illuminated with the laser light by the illumination optical system 40, Projection is performed on the photoresist film PR formed on the wafer W supported by the wafer support unit 21.

  The polarization monitor unit 61 monitors the polarization state of the laser light reflected by the beam splitter 145 in the illumination optical system 40. The polarization monitor 61 includes, for example, a beam splitter (not shown) that splits the laser light reflected from the illumination optical system 40, and a first photodetector (not shown) that detects the laser light that has passed through the beam splitter. A second light detector (not shown) for detecting the laser light reflected by the beam splitter, and using the data of the laser light detected by each of the first light detector and the second light detector, Monitor the polarization state, such as the degree of polarization. Note that each of the first photodetector and the second photodetector is configured by an optical sensor such as a CCD, for example.

  The control unit 71 includes a computer and a memory that stores a program that causes the computer to function as a predetermined unit, and controls each unit. In the present embodiment, the control unit 71 performs illumination optics based on the resist pattern shape information acquired by the resist pattern shape information acquisition unit 81 so that the shape of the resist pattern is formed corresponding to the design pattern. The polarization state adjustment unit 142 of the system 40 is caused to adjust the polarization state of the laser light. Here, the control unit 71 creates a lookup table in which the polarization state value indicated when the laser light source 31 is in a normal state and the value indicating the shape information of the resist pattern formed in the polarization state are associated with each other. The value of the polarization state corresponding to the value of the shape information of the resist pattern acquired by the resist pattern shape information acquisition unit 81 is stored using this lookup table, and the value of the actual polarization state at the time of exposure is stored. Asking. Then, when the obtained actual polarization state value is different from the design condition polarization state value, the polarization state adjustment unit 142 so that the actual polarization state value becomes the design condition polarization state value. A control signal for controlling is generated, and the polarization state adjustment unit 142 adjusts the polarization state of the laser light.

  The resist pattern shape information acquisition unit 81 develops the photoresist film PR onto which the mask pattern image has been projected by the projection optical system 51 with a development processing apparatus (not shown), so that the resist pattern formed on the wafer W can be obtained. Get shape information. For example, in the resist pattern, the resist pattern shape information acquisition unit 81 repeats a line pattern protruding in a convex shape from the surface of the wafer W at a predetermined period across the space, such as a line-and-space pattern. The line width of a repetitive pattern or a line pattern formed so as to be isolated in the resist pattern is measured as resist pattern shape information. That is, the resist pattern shape information acquisition unit 81 measures the CD of the pattern. Here, the resist pattern shape information acquisition unit 91 includes, for example, an image sensor (not shown) such as a CCD, and images the resist pattern formed on the wafer W with the image sensor, and based on the imaging result. As described above, the shape information of the resist pattern is acquired.

(Operation)
Hereinafter, an operation when the exposure apparatus 1 of the present embodiment sets the exposure conditions will be described.

  FIG. 2 is a flowchart showing the main parts of the operation of the exposure apparatus 1 according to the first embodiment of the present invention.

  First, as shown in FIG. 2, exposure is performed (S11).

  Here, the control unit 71 controls each unit to perform exposure so as to correspond to preset exposure setting conditions.

  Specifically, the laser light source 31 emits laser light, and the illumination optical system 40 illuminates the laser light emitted from the laser light source 31 onto the photomask PM supported by the photomask support unit 11. Here, the illumination optical system 40 illuminates so as not to be in a completely linearly polarized state. That is, the control unit 71 controls the polarization state adjusting unit 142 so that the ellipticity of the laser light exceeds 0, and illuminates the photomask PM. This is because the ellipticity can be adjusted in both positive and negative directions when adjusting the polarization state described later.

  Then, the projection optical system 51 projects a mask pattern image generated by the photomask PM illuminated by the illumination optical system 40 onto the photoresist film PM formed on the wafer W supported by the wafer support unit 21. .

  Next, as shown in FIG. 2, acquisition of resist pattern shape information is performed (S21).

  Here, after developing the photoresist film PR on which the mask pattern image is projected by the projection optical system 51, the resist pattern shape information acquisition unit 81 acquires the shape information of the resist pattern formed on the wafer W. In the present embodiment, as the resist pattern shape information, the resist pattern shape information acquisition unit 81 measures the CD value of the formed resist pattern in association with the pattern pitch.

  Next, it is determined whether the polarization state at the time of performing exposure corresponds to the set condition (S31).

  Here, the control unit 71 performs this operation.

  In the present embodiment, first, as described above, the control unit 71 acquires the shape information of the resist pattern formed by actually performing the exposure from the resist pattern shape information acquisition unit 81.

  Then, the resist acquired by the resist pattern shape information acquisition unit 81 from a lookup table in which the polarization state when the laser light source 31 is in a normal state and the shape information of the resist pattern formed in the polarization state are associated with each other. The controller 71 extracts the polarization state corresponding to the pattern shape information.

  Thereafter, the polarization state to be acquired in accordance with the set condition when this exposure is performed is compared with the polarization state extracted from the lookup table.

  Here, when the polarization state to be acquired corresponding to the setting condition is the same as the polarization state extracted from the lookup table, the polarization state at the time of performing the exposure corresponds to the setting condition. Yes (Yes). For example, when the difference is within a predetermined range, it is determined that the polarization states are the same. Then, as shown in FIG. 2, the exposure condition setting process is terminated. Then, the control unit 71 controls each unit so that the next exposure is performed according to the setting conditions set in advance as described above.

  FIG. 3 is a diagram showing a CD simulation result regarding a resist pattern formed corresponding to the pattern pitch P in the polarization state when the laser light source 31 is in a normal state in the embodiment according to the present invention. . Here, a case where a 65 nm line-and-space pattern is formed under illumination conditions with a polarization degree DoP = 1 and a numerical aperture NA = 0.85 is shown, and FIG. 3A shows illumination light. FIG. 3B shows the result of sequentially changing the ellipticity χ of the polarization of the laser light to 0, 0.2, 0.4, 0.6, 0.8, 1.0. This is a result of sequentially changing the principal axis azimuth angle ψ to 0 °, 20 °, 45 °, and 90 °.

  For example, the resist pattern shape information acquisition unit 81 acquires the polarization state setting conditions when the exposure is performed as described above when the ellipticity χ is 0.6 and the principal axis azimuth angle ψ is 45 °. As shown in FIGS. 3 (A) and 3 (B), the resist pattern shape information includes, for example, a CD acquired when the ellipticity χ = 0.6 and the principal axis azimuth angle ψ = 45 °. If it is compatible, it is determined that the exposure is performed in the same polarization state as the setting condition (Yes).

  On the other hand, when the polarization state to be acquired corresponding to the setting condition is different from the polarization state extracted from the lookup table, the polarization state at the time of performing the exposure does not correspond to the setting condition (No). judge.

  For example, when the ellipticity χ is 0.6 and the principal axis azimuth angle ψ is 45 ° under the polarization state setting conditions when performing exposure in the same manner as described above, the laser light emitted from the laser light source 31 is As shown in FIG. 3A and FIG. 3B, the resist pattern shape information acquired by the resist pattern shape information acquisition unit 81 due to the occurrence of an abnormality in which the spectrum width such as the half-value width fluctuates. For example, in the case of a CD acquired when the ellipticity χ = 0.4 and the principal axis azimuth angle ψ = 20 °, it is determined that the exposure is performed in a polarization state different from the setting condition. It is determined that the polarization state at the time of implementation does not correspond to the setting condition (No).

  Then, as shown in FIG. 2, the polarization state of the laser light is adjusted (S41).

  Here, the control unit 81 controls the polarization state adjustment unit 142 of the illumination optical system 40 to adjust the polarization state of the laser light so that the shape of the resist pattern is formed corresponding to the design pattern.

  In the present embodiment, resist pattern shape information acquisition is performed using a lookup table in which the polarization state when the laser light source 31 is in a normal state and the shape information of the resist pattern formed in the polarization state are associated with each other. The control unit 71 calculates a control signal for controlling the polarization state adjustment unit 142 from the shape information of the resist pattern acquired by the unit 81, and causes the polarization state adjustment unit 142 to adjust the polarization state of the laser light.

  Specifically, based on the difference between the polarization state to be acquired corresponding to the setting condition and the polarization state extracted from the lookup table, the setting condition when the exposure is performed is corrected.

  In other words, as described above, when the setting condition of the polarization state at the time of performing the exposure is the ellipticity χ = 0.6 and the principal axis azimuth angle ψ = 45 °, an abnormality has occurred in the laser light source 31. When the resist pattern shape information acquired by the resist pattern shape information acquisition unit 81 is a CD acquired when the ellipticity χ = 0.4 and the principal axis azimuth angle ψ = 20 °, for example, The design conditions are corrected by shifting the original design conditions so as to correspond to the difference values between the ellipticity χ and the principal axis azimuth angle ψ. For example, in this case, the setting condition of the ellipticity χ is shifted from 0.6 to 0.2 which is the difference value and set to 0.8, and the setting condition of the spindle azimuth angle ψ is set to the difference value from 45 °. Is shifted to 25 ° and set to 70 °. Then, each unit is controlled to perform the next exposure under the setting conditions corrected in this way.

  As described above, in the present embodiment, the shape information of the resist pattern formed on the wafer W is acquired by developing the photoresist film PR on which the mask pattern image is projected. And when performing exposure, based on the acquired resist pattern shape information, the laser beam that illuminates the photomask PM is formed so that the shape of the resist pattern is formed corresponding to the design pattern. Adjust the polarization state. Therefore, in the present embodiment, in the laser light emitted from the laser light source 31, even if the spectral width such as the half-value width fluctuates and the chromatic aberration changes, it is efficient that the pattern size after processing varies. Product yield and throughput can be improved.

  In implementing the present invention, the present invention is not limited to the above-described embodiment, and various modifications can be employed.

FIG. 1 is a block diagram showing an exposure apparatus 1 in Embodiment 1 according to the present invention. FIG. 2 is a flowchart showing the main parts of the operation of the exposure apparatus 1 according to the first embodiment of the present invention. FIG. 3 is a diagram showing a simulation result of a CD formed corresponding to the pattern pitch P in the polarization state when the laser light source 31 is in a normal state in the embodiment according to the present invention.

Explanation of symbols

1 ... exposure device,
DESCRIPTION OF SYMBOLS 11 ... Photomask support part, 21 ... Wafer support part, 31 ... Laser light source, 40 ... Illumination optical system, 51 ... Projection optical system, 61 ... Polarization monitor part, 71 ... Control part, 81 ... Resist pattern shape information acquisition part

Claims (4)

An exposure method for performing exposure by irradiating a photomask on which a mask pattern is formed with laser light and projecting a mask pattern image generated by the photomask irradiated with the laser light onto a photoresist film formed on a wafer. There,
A resist pattern shape information obtaining step of obtaining shape information of a resist pattern formed on the wafer by developing the photoresist film on which the mask pattern image is projected,
When performing the exposure, based on the resist pattern shape information acquired in the resist pattern shape information acquisition step, the photo pattern is formed so that the shape of the resist pattern is formed corresponding to a design pattern. An exposure method that adjusts the polarization state of the laser light that illuminates the mask. The exposure method according to claim 1, wherein a main axis azimuth angle and an ellipticity are adjusted as a polarization state of the laser light. An illumination optical system for illuminating the photomask on which the mask pattern is formed with laser light;
A projection optical system for projecting a mask pattern image generated by the photomask illuminated with laser light by the illumination optical system onto a photoresist film formed on a wafer, and the mask pattern image projected by the projection optical system A resist pattern shape information acquiring unit that acquires shape information of a resist pattern formed on the wafer by developing a photoresist film,
The illumination optical system includes a polarization state adjustment unit that adjusts the polarization state of the laser light,
When performing the exposure, the polarization state adjustment unit is configured such that the resist pattern shape acquired by the resist pattern shape information acquisition unit is formed so that the shape of the resist pattern corresponds to a design pattern. An exposure apparatus that adjusts a polarization state of the laser beam based on information. The polarization state adjusting unit includes a quarter-wave plate and a half-wave plate, and each of the quarter-wave plate and the half-wave plate has an optical axis of the laser beam to be illuminated. The polarization state is changed by changing the principal axis azimuth and ellipticity by rotationally driving the quarter wavelength plate and the half wavelength plate. The exposure apparatus according to claim 3 to be adjusted.

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