JP2006086450A - Method of waveform selection, method of position correction, exposure device, and manufacturing method of device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure device which achieves an improvement of an yield by realizing high focusing precision, even in the case of a signal whose detected waveform is asymmetric. <P>SOLUTION: The exposure device carries out a method of waveform selection which irradiates a matter to be exposed with light for detecting the positional waveform of the matter to be exposed and which selects a waveform from the positional waveform. The method comprises a step of detecting a first waveform that is the positional signal from reflected light from the matter, to be exposed in a prescribed detection direction; a step of obtaining a plurality of second waveforms that are the positional signal of a sub detection signal orthogonal to the detection direction, based on the first waveform; a step of deciding whether an unsymmetrical waveform is included in the plurality of second waveforms; and a step of selecting waveforms, excepting for the unsymmetrical waveform, when the unsymmetrical waveform is included in the plurality of second waveforms. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exposure apparatus, and more particularly to an exposure apparatus and method using a waveform selection method for detecting a position waveform of an object to be exposed and selecting the waveform. The present invention is suitable for, for example, a waveform selection method in the case of a signal having asymmetric detection waveforms.

With the recent demand for smaller and thinner electronic devices, projection exposure apparatuses for manufacturing large scale integrated circuits (LSIs) incorporated therein have a higher resolution in reticles with higher integration of semiconductor elements. It is required to project and expose a circuit pattern onto a wafer. The minimum dimension (resolution) that can be transferred by the projection exposure apparatus is proportional to the wavelength of light used for exposure and inversely proportional to the numerical aperture (NA) of the projection optical system. Therefore, the shorter the wavelength, the better the resolution. Therefore, recent light sources include ultra-high pressure mercury lamps (g-line (wavelength: about 436 nm), i-line (wavelength: about 365 nm)) to KrF excimer laser (wavelength: about 248 nm) and ArF excimer laser (wavelength: about 193 nm). Therefore, practical application of F ₂ laser (wavelength of about 157 nm) is also progressing. Furthermore, further expansion of the exposure area is also required.

  In order to achieve these requirements, the exposure area is formed into a rectangular slit shape from a step-and-repeat type exposure apparatus (also called a “stepper”) that reduces the exposure area of a substantially square shape to a wafer and performs batch exposure. For example, a step-and-scan type exposure apparatus (also referred to as a “scanner”) that scans a reticle and a wafer relatively quickly and exposes a large screen with high accuracy is becoming mainstream.

  In the scanner, before the predetermined position of the wafer reaches the exposure slit region during exposure, the surface position at the predetermined position of the wafer is measured by the surface position detecting means of the oblique incidence system, and the predetermined position is determined. Correction is performed to align the wafer surface with the optimum exposure image formation position during exposure.

In particular, in the longitudinal direction of the exposure slit (that is, the direction perpendicular to the scanning direction), in order to measure not only the height (focus) of the surface position of the wafer but also the tilt (tilt) of the surface, a plurality of exposure slit regions are provided. Has measuring points. Many methods for measuring the focus and tilt have been proposed (for example, see Patent Document 1).
JP-A-6-260391

  In recent years, however, the exposure light has become shorter in wavelength and the projection optical system has a higher NA. The depth of focus has become extremely small, and the accuracy of aligning the wafer surface to be exposed to the best imaging plane, the so-called focus accuracy, has increased. It is getting stricter. In particular, the measurement error of the surface position detecting means due to the influence of the pattern on the wafer and the uneven thickness of the resist applied to the wafer cannot be ignored.

  For example, due to uneven thickness of the resist, a large step is generated in the vicinity of the peripheral circuit pattern and the scribe line, although it is smaller than the focal depth, for focus measurement. For this reason, the inclination angle of the resist surface becomes large, and the reflected light detected by the surface position detecting means deviates from the regular reflection angle due to reflection and refraction. Further, due to the difference in density of the pattern on the wafer, a difference in reflectance occurs between the dense pattern area and the rough area. As described above, since the reflection angle and reflection intensity of the reflected light detected by the surface position detecting means change, asymmetry occurs in the detected waveform in which such reflected light is detected, resulting in a measurement error, or the contrast of the detected waveform is reduced. If it significantly decreases, the surface position of the wafer cannot be detected.

  In general, non-uniformity in the pattern step in the wafer surface and uneven thickness of the resist are caused by the wafer process, so that reproducibility within the wafer or between the wafers is poor and offset processing is difficult. Accordingly, the surface position of the wafer cannot be measured during exposure, and exposure stops or large defocusing occurs, resulting in chip failure, thereby reducing yield.

  Therefore, an object of the present invention is to provide an exposure apparatus that achieves high focus accuracy and achieves improved yield even when the detection waveform is an asymmetric signal.

  A waveform selection method according to one aspect of the present invention is a waveform selection method for detecting a position waveform of an object to be exposed by irradiating light to the object to be exposed, and selecting a waveform from the position waveform. Detecting a first waveform as a position signal from reflected light from the body in a predetermined detection direction; and a plurality of position signals as sub-detection directions orthogonal to the detection direction based on the first waveform. Obtaining a second waveform, determining whether an asymmetric waveform is present in the plurality of second waveforms, and when an asymmetric waveform is present in the plurality of second waveforms, Selecting a waveform excluding the asymmetric waveform.

  A position correction method according to another aspect of the present invention detects a position waveform of an object to be exposed by irradiating the object to be exposed, selects a waveform from the position waveform, and corrects the object to be exposed. A position correction method, a step of calculating an ideal waveform that is an ideal waveform of the position waveform, and a step of detecting a first waveform that is a position signal from reflected light from the object to be exposed in a predetermined detection direction. Acquiring a plurality of second waveforms that are position signals in a sub-detection direction orthogonal to the detection direction based on the first waveform; and an asymmetric waveform in the plurality of second waveforms. A step of determining whether there is an asymmetric waveform among the plurality of second waveforms, a step of selecting a waveform excluding the asymmetric waveform, and a difference between the ideal waveform and the selected waveform And correct the first waveform Characterized by a step that.

  An exposure apparatus according to another aspect of the present invention includes a processing unit that performs the waveform selection method.

  A device manufacturing method according to another aspect of the present invention includes a step of exposing an object to be exposed using the above exposure apparatus, and a step of developing the exposed object to be exposed.

  According to the present invention, it is possible to provide an exposure apparatus that achieves high focus accuracy and achieves improved yield even when the detected waveform is an asymmetric signal.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In addition, in each figure, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted. FIG. 1 is a block diagram showing a configuration of an exposure apparatus 1 that uses a waveform selection method 1000.

  The exposure apparatus 1 is a projection exposure apparatus that exposes a circuit pattern formed on a reticle 20 onto a wafer 40 by a step-and-scan method. Such an exposure apparatus is suitable for a lithography process of submicron or quarter micron or less. As shown in FIG. 1, the exposure apparatus 1 includes an illumination apparatus 10, a reticle stage 25 on which the reticle 20 is placed, a projection optical system 30, a wafer stage 45 on which a wafer 40 is placed, and a focus tilt detection system 50. And a control unit 60. The control unit 60 includes a CPU and a memory, and is electrically connected to the illumination device 10, the reticle stage 25, the wafer stage 45, and the focus tilt detection system 50, and controls the operation of the exposure apparatus 1. In this embodiment, the control unit 60 performs a waveform selection method 1000 for optimally setting the waveform of light used when the focus tilt detection system 50 described later detects the surface position of the wafer 40. The waveform selection method 1000 will be described later.

  The illumination device 10 illuminates a reticle 20 on which a transfer circuit pattern is formed, and includes a light source unit 12 and an illumination optical system 14.

The light source unit 12 uses, for example, a laser. Laser, ArF excimer laser having a wavelength of about 193 nm, may be used, such as KrF excimer laser with a wavelength of approximately 248 nm, the kind of light source is not limited to excimer laser, for example, a wavelength of about 157 nm _{F 2} laser or a wavelength 20nm The following EUV (Extreme Ultraviolet) light may be used.

  The illumination optical system 14 is an optical system that illuminates a surface to be illuminated using a light beam emitted from the light source unit 12, and in this embodiment, the light beam is formed into an exposure slit having a predetermined shape optimum for exposure, and the reticle 20 is formed. Illuminate. The illumination optical system 14 includes a lens, a mirror, an optical integrator, a diaphragm, and the like. For example, a condenser lens, a fly-eye lens, an aperture diaphragm, a condenser lens, a slit, and an imaging optical system are arranged in this order. The illumination optical system 14 can be used regardless of on-axis light or off-axis light. The optical integrator includes an integrator configured by stacking a fly-eye lens and two sets of cylindrical lens array (or lenticular lens) plates, but may be replaced by an optical rod or a diffractive element.

  The reticle 20 is made of, for example, quartz, on which a circuit pattern to be transferred is formed, and is supported and driven by the reticle stage 25. Diffracted light emitted from the reticle 20 passes through the projection optical system 30 and is projected onto the wafer 40. The reticle 20 and the wafer 40 are arranged in an optically conjugate relationship. The pattern of the reticle 20 is transferred onto the wafer 40 by scanning the reticle 20 and the wafer 40 at the speed ratio of the reduction magnification ratio. The exposure apparatus 1 is provided with a light oblique incidence type reticle detection means 70, and the position of the reticle 20 is detected by the reticle detection means 70 and is arranged at a predetermined position.

  The reticle stage 25 supports the reticle 20 via a reticle chuck (not shown) and is connected to a moving mechanism (not shown). A moving mechanism (not shown) is configured by a linear motor or the like, and can move the reticle 20 by driving the reticle stage 25 in the X-axis direction, the Y-axis direction, the Z-axis direction, and the rotation direction of each axis.

  The projection optical system 30 has a function of forming an image of a light beam from the object plane on the image plane. In this embodiment, the projection optical system 30 forms an image on the wafer 40 of diffracted light that has passed through the pattern formed on the reticle 20. The projection optical system 30 includes an optical system including only a plurality of lens elements, an optical system (catadioptric optical system) having a plurality of lens elements and at least one concave mirror, a plurality of lens elements, and at least one kinoform. An optical system having a diffractive optical element such as can be used. When correction of chromatic aberration is required, a plurality of lens elements made of glass materials having different dispersion values (Abbe values) can be used, or the diffractive optical element can be configured to generate dispersion in the opposite direction to the lens element. To do.

  The wafer 40 is an object to be processed, and a photoresist is applied on the substrate. In the present embodiment, the wafer 40 is also a detected object whose position is detected by the focus tilt detection system 50. In another embodiment, the wafer 40 is replaced with a liquid crystal substrate or other object to be processed.

  The wafer stage 45 supports the wafer 40 by a wafer chuck (not shown). Similar to reticle stage 25, wafer stage 45 uses a linear motor to move wafer 40 in the X-axis direction, Y-axis direction, Z-axis direction, and the rotational direction of each axis. Further, the position of the reticle stage 25 and the position of the wafer stage 45 are monitored by, for example, a laser interferometer or the like, and both are driven at a constant speed ratio. The wafer stage 45 is provided on a stage surface plate supported on a floor or the like via a damper, for example, and the reticle stage 25 and the projection optical system 30 are, for example, on a base frame placed on the floor or the like. It is provided on a lens barrel surface plate (not shown) that is supported via a damper.

  In this embodiment, the focus tilt detection system 50 detects position information of the surface position (Z-axis direction) of the wafer 40 during exposure using an optical measurement system. The focus tilt detection system 50 makes a light beam incident on a plurality of measurement points to be measured on the wafer 40, guides each light beam to an individual sensor, and calculates the tilt of the surface to be exposed from position information (measurement results) at different positions. To detect.

  As shown in FIG. 2, the focus tilt detection system 50 detects an image shift of reflected light reflected from the surface of the wafer 40 and an illumination unit 52 that makes a light beam incident on the surface of the wafer 40 at a high incident angle. A unit 54 and a calculation unit 56. The illumination unit 52 includes a light source 521, light combining means (not shown), a pattern plate 523, an imaging lens 524, and a mirror 525. The detection unit 54 includes a mirror 541, a lens 542, an optical demultiplexing unit (not shown), and a light receiver 544. Here, FIG. 2 is an enlarged block diagram showing a configuration of the focus tilt detection system 50. In FIG. 2, illustrations of lenses necessary for illuminating the pattern plate 523 with a uniform illuminance distribution in the illumination unit 52 and lenses for correcting chromatic aberration in the detection unit 54 are omitted.

  Referring to FIG. 2, light having a wavelength λ emitted from a light source 521 such as an LED or a halogen lamp passes through a light synthesizing unit including a mirror or a dichroic mirror, and a pattern plate on which a pattern such as a slit is formed. Illuminate 523. The light that has passed through the pattern plate 523 is projected and imaged on the wafer 40 via the imaging lens 524 and the mirror 525.

  Further, the light reflected by the wafer 40 is received by a light receiver 544 including a light receiving element such as a CCD element or a line sensor via a mirror 541 and a lens 542. Note that an optical demultiplexing unit including a mirror and a dichroic mirror is disposed in front of the light receiver 544. The optical demultiplexing means has a function of dividing light of different wavelengths so that the light from the light source 521 is received by the light receiving element 544. The pattern image on the surface of the wafer 40 of the pattern plate 523 is re-imaged on the light receiving element 544 by the lens 542.

  When the wafer 40 moves in the vertical direction (that is, the Z-axis direction) via the wafer stage 45, the pattern image of the pattern plate 523 moves in the left-right direction (that is, the X-axis direction) on the light receiver 544. Therefore, the focus tilt detection system 50 detects the position of the surface of the wafer 40 for each measurement point by calculating the position of the pattern image with the calculation unit 56.

  Here, the relationship between the pattern on the pattern plate 523 and the signal waveform detected by the detection unit 54 will be described. FIG. 3 is a plan view showing an example of the pattern plate 523. The pattern plate 523 includes a light shielding region 523a that blocks light and a transmission pattern 523b that transmits light, and the transmission pattern 523b has a rectangular shape. Further, the pattern plate 523 is formed so that the light to be illuminated has a predetermined angle with respect to the pattern of the wafer 40 as shown in FIG. This is to distinguish between the detection signal of the pattern formed on the wafer 40 and the detection signal of the pattern plate 523 when detecting the detection signal of the pattern plate 523. The setting of the angle of the pattern plate 523 will be described later together with the waveform selection method 1000. Here, FIG. 4A is a plan view showing the wafer 40, and FIG. 4B is an enlarged plan view of the wafer 40.

  In this case, since the pattern plate 523 has a predetermined angle, the light that illuminates the pattern plate 523 is reflected across patterns having different reflectivities. As a result, as shown in FIG. 4B, symmetrical waveforms are detected in the cross sections AA ′ and CC ′ of the symmetric regions β1 and β3. On the other hand, since the cross section BB ′ of the asymmetric region β2 straddles patterns with different reflectivities, an asymmetric waveform is detected. As a result, a graph as shown in FIG. 5 is obtained. Here, FIG. 5 is a graph in which the reflectance of the pattern plate 523 is measured. As shown in FIG. 5, the reflectance changes at the position of the cross section BB ′. Thereby, a waveform having asymmetry is detected. The difference in reflectance on the wafer 40 occurs mainly due to the difference in pattern density (line width and pitch) and vertical structure at the boundary portion such as the memory cell portion, the peripheral circuit portion, and the scribe line. There are many.

  Further, the asymmetry of the waveform of the wafer 40 is caused not only by the wafer patterns having different reflectivities but also by simple non-uniform film thickness of the resist 42.

  Here, with reference to FIG. 6, the dependence of the waveform signal detected by the detection unit 54 on the wavelength of the light to be illuminated will be described. FIG. 6 is a diagram for explaining the difference in reflectance caused by the film thickness non-uniformity of the resist 42 due to the pattern step 41 on the wafer 40. The reflectance of the wafer 40 coated with the resist 42 is determined by the interference between the reflected light of the resist surface 42a and the reflected light of the resist back surface (that is, the interface between the wafer 40 and the resist 42) 42b. Since the film thickness Rt ′ of the resist 42 in the region E2 with the pattern step 41 is thicker than the film thickness Rt of the resist 42 in the region E1 without the pattern step 41 on the wafer 40, the light irradiated to the region E1 The difference in optical path length between the reflected light ka1 on the resist surface 42a and the reflected light ka2 on the resist back surface 42b, and the difference in optical path length between the reflected light kb1 on the resist surface 42a and the reflected light kb2 on the resist back surface 42b of the light irradiated to the region E2. Different. As a result, a difference occurs in the reflectance between the region E1 and the region E2. When light is irradiated on a region having such a difference in reflectance, an asymmetric signal waveform is generated.

  Hereinafter, the waveform selection method 1000 will be described with reference to FIG. FIG. 12 is a flowchart for explaining the waveform selection method 1000. The waveform selection method 1000 is a method of detecting a position waveform of the wafer 40 by irradiating light onto the wafer 40 and selecting a symmetrical waveform from the position waveform.

  First, a surface position signal (first waveform) is detected from the reflected light from the wafer 40 in a predetermined scanning direction (step S1002).

  Hereinafter, in FIG. 4B, the rotation angle A of the irradiation projection pattern image 523t ′ of the slit plate 523 onto the wafer 40 (the angle formed with the Y axis when the scanning direction of the exposure apparatus is the Y axis, the unit is “degree”). ”), The optimum conditions for the width Wα in the scanning direction α and the width Wβ in the slit longitudinal direction β of the irradiation projection pattern image 523t ′ will be described. The IC circuit pattern in the shot has a directionality that there are many patterns parallel to the X / Y direction which is the shot arrangement direction. Therefore, as shown in FIG. 4B, the boundary line E where the reflectance changes is also parallel to the X / Y axis, and is parallel to the boundary line E and the non-measurement direction (β) of the irradiation projection pattern image 523t ′. A region between the intersections of the two sides (L and R) is an asymmetric signal generation region. The length β2 of the asymmetrical region in the slit longitudinal direction is β2 = Wα · tanA. In the present invention, since it is preferable that there is a region having a uniform reflectance, the condition in which the length Wβ in the slit longitudinal direction is longer than β2, that is, the following Equation 1 is one preferable condition.

  On the other hand, FIG. 4B shows the case where the boundary line E of the reflectance is parallel to the Y axis, but the boundary line E may be parallel to the X axis. In this case, since the length β2 of the asymmetric region in the slit longitudinal direction is β2 = Wα · tan (90−A), the following formula 2 is obtained as the second preferable condition.

  In this way, the rotation angle A of the irradiation projection pattern image 523t ′, the width Wα in the scanning direction, and the width Wβ in the slit longitudinal direction are determined so as to satisfy Equation 1 and Equation 2 at the same time. (Detection system) 50 pattern plate 523, illumination system, and exposure apparatus are preferably configured. Equations 1 and 2 show conditions under which a region with uniform reflectivity is the lowest, and more preferably, a condition in which a symmetric region and an asymmetric region are equivalent, that is, twice Wβ that simultaneously satisfies Equations 1 and 2. It is preferable to determine the rotation angle of the irradiation projection pattern image 523t ′, the width in the scanning direction, and the width in the longitudinal direction of the slit so that the value becomes. Since the reflectance boundary line E on the wafer is considered to be probabilistically equivalent with respect to the X axis and the Y axis, there is no difference between Expression 1 and Expression 2 as the rotation angle of the irradiation projection pattern image 523t ′. That is, it can be said that the vicinity of 45 degrees is preferable.

  Here, the measurement points of the surface position (focus) of the wafer 40 will be described. In the present embodiment, as shown in FIG. 7, a total of 21 measurement points KP of 7 points in the scanning direction and 3 points in the direction perpendicular to the scanning direction (slit longitudinal direction) with respect to the exposure area EE1 of one shot. have. Two focus tilt detection systems 50 shown in FIG. 2 are arranged in the slit longitudinal direction (X-axis direction) to measure three measurement points KP in the slit longitudinal direction, and the wafer stage 45 is scanned in the Y-axis direction. It is configured to be able to measure 7 measurement points in the scan direction (Y-axis direction). Here, FIG. 7 is a plan view showing an example of the arrangement of the measurement points KP on the wafer 40.

  Further, as shown in FIG. 8, in order to expose a plurality of shots on the wafer 40, the wafer stage 45 is stepped or scanned for each shot, and measurement is performed on the 21 measurement points KP shown in FIG. As shown in FIG. 9, the measurement point KP in the longitudinal direction of the slit is required to obtain the tilt amount ωy of the wafer 40 in the longitudinal direction of the slit, so two or more measurement points KP are necessary. Further, when it is necessary to measure the tilt amount ωx of the wafer 40 in the scan direction within the slit, as shown in FIG. 10, the measurement point KP at a different position in the scan direction within the slit and the corresponding focus tilt detection system 50 must be provided. Here, FIG. 8 is a plan view showing a shot layout on the wafer 40. 9 and 10 are plan views showing an example of the arrangement of the measurement points KP in the slits on the wafer 40. FIG.

  Returning to FIG. 12, a plurality of waveforms (second waveforms) which are position signals in the slit longitudinal direction orthogonal to the scanning direction are acquired based on the position waveform (step S1004). In the present embodiment, the waveform in the slit longitudinal direction at the cross sections AA ′ and CC ′ of the symmetric regions β1 and β3 and the waveform in the slit longitudinal direction of the cross section BB ′ of the asymmetric region β2 shown in FIG. . As shown in FIG. 11, the acquired waveform shows that the cross section AA ′ and the cross section CC ′ show a symmetric waveform, and the cross section BB ′ shows an asymmetric waveform.

  In the present embodiment, for the sake of simplicity, the number of divided measurements in the slit longitudinal direction has been described as three. However, the number of division measurements can be increased up to the number of pixels in the slit longitudinal direction of the sensor to be used at the maximum, and about 10-20 divisions using an average (integrated) signal of a plurality of lines in consideration of the throughput. Preferably, a signal is generated. Further, the same effect can be obtained by calculating the position of each waveform of the symmetric signal and using the average value instead of generating the integrated signal waveform of the symmetric signal. Here, FIG. 11 is a graph obtained by measuring the reflectance of the wafer.

  Next, it is determined whether or not there is an asymmetric waveform among the plurality of waveforms acquired in step S1004 (step S1006). If it is determined in step S1006 that an asymmetric waveform exists among the plurality of waveforms, a waveform excluding the asymmetric waveform is selected (step S1008). Here, it is determined whether each of the acquired plurality of waveforms has a predetermined threshold value, and only waveforms having the predetermined threshold value are selected. The threshold value here is set depending on the surface position detection accuracy of the device user. The setting of the threshold value in this case can be determined based on the signal intensity including the peak intensity or the integrated intensity. That is, the intensity change in the non-measurement direction of the two-dimensional sensor can be evaluated.

  FIG. 13 is a plot of the peak intensity of the signal of FIG. 5 with respect to the non-measurement direction, and at the same time, the difference (rate of change) from the adjacent measurement line is plotted on the right axis. As described above, the signal intensity (peak intensity and integrated light quantity) is constant in the symmetric signal area, whereas the signal intensity changes abruptly in the asymmetric signal area. In the figure, a threshold is set at 1% of the intensity change in the non-measurement direction, and the center-of-gravity calculation process is performed using a signal within the range (a signal exceeding the threshold is not used). This threshold is preferably set in the range of 1% to 5% in accordance with the accuracy required by the user. Here, FIG. 13 is a graph showing the light intensity of the wafer 40 and the intensity change.

  The setting of another threshold is determined by calculating a plurality of midpoints of a plurality of waveforms acquired in accordance with the reflectance and evaluating variations in the plurality of midpoints. For example, when the relationship when the detection magnification of the acquired waveform is M, the surface position fluctuation of the wafer 40 is dz, and the position fluctuation in the position detection device is dx satisfies dx = M · dz, the threshold in that case is In the preferred embodiment, when the required accuracy of the surface position detection is Zr, it is set to M · Zr.

  FIG. 14 shows an example of a signal obtained by normalizing the waveform signal of the cross section BB ′ of FIG. 11 which is an example of a signal at a certain measurement point in the sample shot so that the peak intensity becomes 1. In FIG. Here, FIG. 14 is a graph showing the reflectance of the wafer and the position on the sensor.

  As shown in the figure, the left and right intersections Li and Ri of the slice level and the signal are obtained, the midpoint Mi is further obtained, and the midpoint Mi when the slice level is changed from 0.2 to 0.9 is obtained. Each is obtained and the variation of the midpoint Mi when the slice level is changed is obtained (3σ or range).

  A method is adopted in which a signal in which the variation amount is equal to or less than a predetermined threshold is determined as a symmetric signal.

Still another threshold setting is determined by evaluating the symmetry of the left and right slopes of the acquired waveform. As shown in FIG. 15, the slope component of a predetermined region of a signal (region where the slice level is 0.2 to 0.8 in the figure) is obtained, and the difference between the absolute values falls within a predetermined threshold. It may be determined that the signal waveform is correct. If the threshold is set strictly, only a more symmetric signal is selected, and the measurement error due to asymmetry is reduced. May get worse. As a result of evaluating this threshold experimentally, it was found that the threshold of the difference between the absolute values of the slopes is preferably in the range of 1% to 10%.
In this way, it is the essence of the present invention to reduce the measurement error by providing a certain threshold value and removing the asymmetric signal distorted larger than the threshold value. Therefore, the optimal formulas 1 and 2 for the rotation angle of the irradiation projection pattern image 523t ′, the width in the measurement direction of the irradiation projection pattern image 523t ′, and the width in the non-measurement direction described above are preferable conditional expressions. It will be supplemented here that the description is not intended to limit the gist of the present invention. Here, FIG. 15 is a graph showing the reflectance of the wafer 40 and the position on the sensor.

  The measured value M1 (i, j) using the signal only in the symmetric area is calculated by the above-described method. Here, (i, j) indicates measurement points in the shot shown in FIG. In the present invention, the center-of-gravity detection method is used as a signal processing method for obtaining the position of the signal waveform. When using the center-of-gravity detection method, the top and bottom portions of the signal are easily affected by noise. For example, as shown in FIG. 15, using a portion between slice levels 0.2 to 0.8, It is preferable to calculate the centroid and obtain the centroid pixel. In this way, the operation of extracting the symmetric signal region in the non-measurement direction is performed for each measurement point (i, j), and the processing range (symmetric extraction range) for each measurement point (i, j). ) Is registered in the exposure apparatus, and from the next wafer, signal processing is performed based on the processing range registered on the apparatus to obtain a measured value. In this embodiment, for each shot of the sample shot, a symmetric area of the measurement point (i, j) is calculated, and an area that is commonly included in all 14 sample shots is registered in the exposure apparatus as a processing area. I have to.

  Note that the number of sample shots used to extract a processing region that becomes a symmetric signal is not limited to 14, but it is possible to measure all shots on a wafer from at least one sample. It is also possible to increase the extraction accuracy of the symmetric region by measuring not only one but several wafers and increasing the parameter. Furthermore, if the exposure apparatus user knows the structure of the wafer pattern in the shot in advance, the information and the irradiation position on the wafer of the pattern plate 523 are collated, so that the exposure apparatus user corresponds to the position in the shot. Since a processing area for generating a symmetric signal can be determined, it is also possible to input and register the processing area in the exposure apparatus. In this case, a preceding wafer is not necessary.

  Further, in the present embodiment, the pattern plate 523 is configured such that light is transmitted through the light shielding region 523a, but conversely, only the light shielding region portion is formed using the entire surface of the pattern plate as the transmission portion. A configuration in which light is shielded may be used, or a pattern in which a plurality of grids are arranged may be used, and this example may be implemented for each pattern to use an average value of measured values at a plurality of pattern positions. .

  Next, an outline of the surface position correction of the wafer 40 by measuring the focus and tilt at the time of scan exposure will be described. As shown in FIG. 16, measurement points KP (measurement positions FP) arranged at a plurality of points so as to form a plane in front of the exposure slit before the wafer 40 having an uneven shape in the scanning direction reaches the exposure position EP. The focus of the surface position of the wafer 40 and the tilt (hereinafter referred to as “tilt X”) in the longitudinal direction of the exposure slit region (that is, the direction perpendicular to the scanning direction) are measured. Then, based on the position information detected by the focus tilt detection system 50, the wafer stage 45 is driven to perform correction driving to the exposure position EP. For example, in FIG. 2, the surface position at the position of j = 7 is measured while the position of j = 6 on the wafer 40 is exposed. Then, after the exposure at the position of j = 6 is completed, the exposure at the position of j = 7 is performed while correcting and driving the focus and tilt X based on the measurement result of the surface position of the position of j = 7. Here, FIG. 16 is a perspective view showing the exposure area EP and the focus and tilt measurement positions FP on the wafer 40.

  According to the waveform selection method 1000 described above, high focus accuracy can be realized even when the detected waveform is an asymmetric signal. As a result, the exposure apparatus 1 that uses the waveform selection method 1000 of this embodiment can perform high-precision exposure.

  The second embodiment of the exposure apparatus according to the present invention will be described below. This embodiment is different from the first embodiment in the focus and tilt detection system, and has a two-dimensional area sensor and a one-dimensional line sensor.

  The configuration and operation of the focus tilt detection system (surface position detection system) 50 of this embodiment will be described in detail. FIG. 17 is an enlarged block diagram showing another configuration of the focus tilt detection system 50.

  In the figure, light emitted from a light source 521 (such as an LED or a halogen lamp) illuminates a pattern plate 523 on which a pattern such as a slit is formed. A pattern plate 523 (same as that used in the first embodiment shown in FIG. 2) is projected and imaged onto the wafer 40 via an imaging lens 524 and a mirror 525.

  Further, the light reflected by the wafer 40 is received by the light receiver 544A via the mirror 541 and the lens 542. The pattern image on the wafer surface of the pattern plate 523 is re-imaged on the area sensor 544B by the lens 542. In the figure, reference numeral 20 denotes a mirror, which is used for switching the optical path of the reflected light from the wafer.

  The mirror 543 has a function of switching between the area sensor 544B and the line sensor 544A. Even in a configuration in which the mirror 543B is extracted in the optical path, a part of the wafer reflected light is reflected and guided to the area sensor 544B using a beam splitter. A configuration may be adopted in which part of the wafer reflected light is transmitted and guided to the line sensor 544A.

  The light traveling straight without being reflected by the mirror 543 is condensed in the non-measurement direction by the cylindrical lens 545 having power in the non-measurement direction, and an image of the pattern plate 523 is re-imaged on the line sensor 544.

  Next, how to use the area sensor 544B and the line sensor 544A will be described.

  First, a preceding wafer on which a base pattern is patterned and a resist is coated thereon is loaded onto an exposure apparatus. Subsequently, in the wafer shot layout of FIG. 8, the wafer surface position of the 14-shot sample shot is measured by both the area sensor 544B and the line sensor 544A of the focus detection system.

  Next, a symmetric area is extracted based on the measurement data of the area sensor 544B as in the first embodiment, and a measurement value M1 (i, j) using a signal only for the symmetric area is calculated. Subsequently, a measurement value M2 (i, j) is obtained based on the measurement data of the line sensor 544A. Here, (i, j) indicates measurement points in the shot shown in FIG. The signal processing method is the same centroid detection method as in the previous embodiment. At this time, when a difference value dM (i, j) = M1 (i, j) −M2 (i, j) between two measurement values at each measurement point (i, j) is obtained, this value is calculated by the line sensor. This corresponds to a measurement error due to the wafer pattern included in the measurement value of 544B.

  In this way, dM (i, j) obtained from the difference value between the two sensor outputs is stored as an offset amount at each measurement point (i, j), and the measurement value of the line sensor 544A is measured from the next wafer. dM2 (i, j) + dM (i, j) obtained by adding the offset amount dM (i, j) stored on the apparatus to dM2 (i, j) is used as the measurement value.

  Note that the number of sample shots used in this embodiment is not limited to 14, and all shots on the wafer may be measured from at least one. Furthermore, the number of wafers to be measured is not limited to one, but several The wafer may be measured. That is, when there are N sample shots, the offset amount dM (i, j) of the measurement point (i, j) is calculated for each shot, and the average value of the N sample shots is obtained and registered in the exposure apparatus. Like to do.

  As described above, in the present embodiment, the measurement position (i, i) in the shot of the line sensor 544A is obtained in advance by using the signal of only the symmetric area of the area sensor 544B and the processing result of the signal of the line sensor 544A. The measurement error amount in j) is registered as an offset, and since the offset and the processing result of the line sensor 544A are used from the next wafer, the processing of the area sensor signal can be omitted, and the processing can be performed as compared with the first embodiment. Time can be shortened, and the throughput of the exposure apparatus can be improved.

  The third embodiment will be described with reference to FIG. The present embodiment is different from the above-described embodiment in the focus tilt detection system, and has a feature in the configuration of the pattern plate 523 that can be arbitrarily divided and illuminated in the non-measurement direction on the illumination system side. The other apparatus configuration is the same as that in FIG. 2 or FIG. 17, and will be described with reference to FIG. 17 in the following description. The pattern plate 523A in FIG. 17 has a liquid crystal cell array structure as shown in FIG. 18, and controls the voltage applied to an arbitrary cell as shown in FIG. The liquid crystal shutter array does not transmit the light.

Next, a method for using the liquid crystal shutter array will be described. First, a preceding wafer on which a base pattern is patterned and a resist is coated thereon is loaded onto an exposure apparatus. Subsequently, in the wafer shot layout of FIG. 8, the wafer surface position of 14 sample shots is measured by the area sensor 544B of the focus detection system.
Next, based on the measurement data of the area sensor 544B, a symmetric signal region is extracted as in the first embodiment. At this time, a symmetric signal region is extracted for each measurement point (i, j), and a symmetric region of the measurement point (i, j) is calculated for each shot of the sample shot, and all of the N sample shots are calculated. Are registered in the exposure apparatus as a measurement target area. From the next wafer, the liquid crystal shutter array is controlled so as to correspond to the measurement target area for each measurement point (i, j) registered in the exposure apparatus so that light is irradiated only to the measurement target area. To do. Reflected light from the wafer is received by the line sensor 544A, the position of the signal waveform of the line sensor 544A is detected, and the surface position of the wafer is obtained.

  Thus, in this embodiment, the area to be measured is selected in advance by using the area sensor 544B with the preceding wafer, and the measurement position (i, j) in the shot is selected corresponding to the measurement position (i, j). By illuminating only the measurement target area with the liquid crystal shutter array, only the processing of the line sensor 544A is performed as the signal processing from the next wafer. Compared to the embodiment, the processing time can be shortened and the throughput of the exposure apparatus can be improved.

  In the exposure, the EUV light emitted from the illumination device 110 illuminates the mask 120 by an optical element arranged in a vacuum environment, and forms an image of the pattern on the surface of the mask 120 on the surface of the object to be exposed 140. In the present embodiment, the image plane is an arc-shaped (ring-shaped) image plane, and the entire surface of the mask 120 is exposed by scanning the mask 120 and the exposure target 140 at a speed ratio of the reduction ratio. Further, since the exposure apparatus 1 of the present embodiment uses the waveform selection method 1000, it can perform high-precision exposure. Needless to say, a position detection apparatus having a processing unit (in this embodiment, the function of the control unit 60) capable of performing the waveform selection method 1000 also constitutes one aspect of the present invention.

  Next, an embodiment of a device manufacturing method using the above-described exposure apparatus 1 will be described with reference to FIGS. FIG. 19 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like). Here, the manufacture of a semiconductor chip will be described as an example. In step 1 (circuit design), a device circuit is designed. In step 2 (mask production), a mask on which the designed circuit pattern is formed is produced. In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the mask and the wafer. Step 5 (assembly) is called a post-process, and is a process for forming a semiconductor chip using the wafer created in step 4. The assembly process (dicing, bonding), packaging process (chip encapsulation), and the like are performed. Including. In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 5 are performed. Through these steps, a semiconductor device is completed and shipped (step 7).

  FIG. 20 is a detailed flowchart of the wafer process in Step 4. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. Step 14 (ion implantation) implants ions into the wafer. In step 15 (resist process), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the exposure apparatus 1 to expose a circuit pattern on the mask onto the wafer. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeatedly performing these steps, multiple circuit patterns are formed on the wafer. According to the device manufacturing method of the present embodiment, it is possible to manufacture a higher quality device than before.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist.

It is a schematic block diagram which shows the structure of the exposure apparatus which uses a waveform selection method. FIG. 2 is an enlarged block diagram showing a configuration of a focus tilt detection system of the exposure apparatus shown in FIG. 1. It is a schematic plan view which shows an example of the pattern board of the focus tilt detection system shown in FIG. It is a schematic plan view which shows a wafer. It is the graph which measured the reflectance of the wafer. It is a figure for demonstrating the difference of the reflectance resulting from the film thickness nonuniformity of the resist by the pattern level | step difference on a wafer. It is a schematic plan view which shows an example of arrangement | positioning of the measurement point KP on a wafer. It is a schematic plan view which shows the shot layout on a wafer. It is a schematic plan view which shows an example of arrangement | positioning of the measurement point KP in the slit on a wafer. It is a schematic plan view which shows an example of arrangement | positioning of the measurement point KP in the slit on a wafer. It is the graph which measured the reflectance of the wafer. It is a flowchart for demonstrating the waveform selection method. It is a graph which shows the optical intensity and intensity | strength change of a wafer. It is a graph which shows the reflectance on a wafer, and the position on a sensor. It is a graph which shows the reflectance on a wafer, and the position on a sensor. It is a schematic perspective view which shows exposure position EP and the measurement position FP of the focus and tilt on a wafer. It is an enlarged block diagram which shows another structure of the focus tilt detection system shown in FIG. It is a schematic plan view which shows another example of the pattern board shown in FIG. 2 is a flowchart for explaining the manufacture of a device (a semiconductor chip such as an IC or LSI, an LCD, a CCD, or the like) using the EUV exposure apparatus of the present invention shown in FIG. 20 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 19.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exposure apparatus 10 Illumination apparatus 20 Reticle 30 Projection optical system 40 Wafer 50 Focus tilt detection system 52 Illumination part 521 Light source 523 Pattern board 54 Detection part 60 Control part

Claims (10)

A waveform selection method for irradiating light to an object to be exposed to detect a position waveform of the object to be exposed, and selecting a waveform from the position waveform,
Detecting a first waveform as a position signal from reflected light from the object to be exposed in a predetermined detection direction;
Obtaining a plurality of second waveforms that are position signals in a sub-detection direction orthogonal to the detection direction based on the first waveform;
Determining whether there is an asymmetric waveform among the plurality of second waveforms;
And a step of selecting a waveform excluding the asymmetric waveform when an asymmetric waveform is present in the plurality of second waveforms. 2. The determination step according to claim 1, wherein the determination step determines based on a signal intensity including a peak intensity or an integrated intensity, and determines that the waveform is an asymmetric waveform when a change in the signal intensity exceeds a predetermined threshold. Waveform selection method. 3. The waveform selection method according to claim 2, wherein the threshold is set to 1 to 5%. The determining step includes calculating a plurality of midpoints of the second waveform according to the reflectance of the reflected light;
Evaluating the variation of the plurality of midpoints;
2. The waveform selection method according to claim 1, further comprising the step of determining that the signal is a symmetric signal if it is equal to or less than a predetermined threshold value. When the relationship when the position waveform detection magnification is M, the surface position fluctuation of the object to be exposed is dz, and the position fluctuation in the position detection apparatus is dx satisfies dx = M · dz, the threshold value is: 5. The waveform selection method according to claim 4, wherein M / Zr is set when the required detection accuracy is Zr. 2. The waveform selection method according to claim 1, wherein the determining step evaluates the symmetry of the left and right slopes of the second waveform, and determines that the signal is a symmetric signal if it is equal to or less than a predetermined threshold. The waveform selection method according to claim 6, wherein the threshold is set to 1 to 10%. A position correction method for detecting a position waveform of the object to be exposed by irradiating the object to be exposed, selecting a waveform from the position waveform, and correcting the object to be exposed,
Calculating an ideal waveform which is an ideal waveform of the position waveform;
Detecting a first waveform as a position signal from reflected light from the object to be exposed in a predetermined detection direction;
Obtaining a plurality of second waveforms that are position signals in a sub-detection direction orthogonal to the detection direction based on the first waveform;
Determining whether there is an asymmetric waveform among the plurality of second waveforms;
If an asymmetric waveform is present in the plurality of second waveforms, selecting a waveform excluding the asymmetric waveform;
A position correction method comprising: calculating a difference between the ideal waveform and the selected waveform and correcting the first waveform. An exposure apparatus comprising: a processing unit that performs the waveform selection method according to claim 1. Exposing an object to be exposed using the exposure apparatus according to claim 9;
And developing the exposed object to be exposed.